Browsing by Author "Wonkam, Ambroise"

Now showing 1 - 20 of 35
  • Thumbnail Image
    Item
    Open Access
    Age Estimate of GJB2-p.(Arg143Trp) Founder Variant in Hearing Impairment in Ghana, Suggests Multiple Independent Origins across Populations
    (2022-03-21) Aboagye, Elvis Twumasi; Adadey, Samuel Mawuli; Esoh, Kevin; Jonas, Mario; de Kock, Carmen; Amenga-Etego, Lucas; Awandare, Gordon A; Wonkam, Ambroise
    Gap junction protein beta 2 (GJB2) (connexin 26) variants are commonly implicated in non-syndromic hearing impairment (NSHI). In Ghana, the GJB2 variant p.(Arg143Trp) is the largest contributor to NSHI and has a reported prevalence of 25.9% in affected multiplex families. To date, in the African continent, GJB2-p.(Arg143Trp) has only been reported in Ghana. Using wholeexome sequencing data from 32 individuals from 16 families segregating NSHI, and 38 unrelated hearing controls with the same ethnolinguistic background, we investigated the date and origin of p.(Arg143Trp) in Ghana using linked markers. With a Bayesian linkage disequilibrium gene mapping method, we estimated GJB2-p.(Arg143Trp) to have originated about 9625 years (385 generations) ago in Ghana. A haplotype analysis comparing data extracted from Ghanaians and those from the 1000 Genomes project revealed that GJB2-p.(Arg143Trp) is carried on different haplotype backgrounds in Ghanaian and Japanese populations, as well as among populations of European ancestry, lending further support to the multiple independent origins of the variant. In addition, we found substantial haplotype conservation in the genetic background of Ghanaian individuals with biallelic GJB2- p.(Arg143Trp) compared to the GJB2-p.(Arg143Trp)-negative group with normal hearing from Ghana, suggesting a strong evolutionary constraint in this genomic region in Ghanaian populations that are homozygous for GJB2-p.(Arg143Trp). The present study evaluates the age of GJB2-p.(Arg143Trp) at 9625 years and supports the multiple independent origins of this variant in the global population.
  • Thumbnail Image
    Item
    Open Access
    Association of variants at BCL11A and HBS1L-MYB with hemoglobin F and hospitalization rates among sickle cell patients in Cameroon
    (Public Library of Science, 2014) Wonkam, Ambroise; Bitoungui, Valentina J Ngo; Vorster, Anna A; Ramesar, Raj; Cooper, Richard S; Tayo, Bamidele; Lettre, Guillaume; Ngogang, Jeanne
    BACKGROUND: Genetic variation at loci influencing adult levels of HbF have been shown to modify the clinical course of sickle cell disease (SCD). Data on this important aspect of SCD have not yet been reported from West Africa. We investigated the relationship between HbF levels and the relevant genetic loci in 610 patients with SCD (98% HbSS homozygotes) from Cameroon, and compared the results to a well-characterized African-American cohort. Methods and FINDINGS: Socio-demographic and clinical features were collected and medical records reviewed. Only patients >5 years old, who had not received a blood transfusion or treatment with hydroxyurea were included. Hemoglobin electrophoresis and a full blood count were conducted upon arrival at the hospital. RFLP-PCR was used to describe the HBB gene haplotypes. SNaPshot PCR, Capillary electrophoresis and cycle sequencing were used for the genotyping of 10 selected SNPs. Genetic analysis was performed with PLINK software and statistical models in the statistical package R. Allele frequencies of relevant variants at BCL11A were similar to those detected in African Americans; although the relationships with Hb F were significant (p <.001), they explained substantially less of the variance in HbF than was observed among African Americans (∼ 2% vs 10%). SNPs in HBS1L-MYB region ( HMIP ) likewise had a significant impact on HbF, however, we did not find an association between HbF and the variations in HBB cluster and OR51B5/6 locus on chromosome 11p, due in part to the virtual absence of the Senegal and Indian Arab haplotypes. We also found evidence that selected SNPs in HBS1L-MYB region ( HMIP ) and BCL11A affect both other hematological indices and rates of hospitalization. CONCLUSIONS: This study has confirmed the associations of SNPs in BCL11A and HBS1L-MYB and fetal haemoglobin in Cameroonian SCA patients; hematological indices and hospitalization rates were also associated with specific allelic variants.
  • Thumbnail Image
    Item
    Open Access
    Association of variants in APOL1, MYH9 and HMOX1 WITH micro-Albuminuria among Sickle Cell disease patients from Cameroon
    (2016) Geard, Amy; Wonkam, Ambroise; Chimusa, Emile R
    Introduction: Sickle Cell Disease (SCD) is a monogenic, multi-organ hemoglobinopathy disorder that is highly prevalent in Africa, with nearly 300 000 newborn cases per year. The underlying pathophysiological mechanism of the disease involves alteration of the normal soft and biconcave disc shape of erythrocytes, to that of a rigid crescent. These abnormal red blood cells cause vaso-occlusion and intravascular hemolysis, resulting in a variety of clinical manifestations, including acute pain crises, anemia, and damage to various organs. Kidney disease is a clinical proxy of severity, developing only in a subset of patients, and is subject to modification by genetic variations. Indeed, reports have shown significant association between proteinuria and specific genetic variants in MYH9 and APOL1, and between estimated Glomerular Filtration Rate (eGFR) and End Stage Kidney Disease (ESKD) with HMOX1 variants among adult African Americans affected by SCD. However, the association between these variants and micro-albuminuria, a primary indicator of renal dysfunction, has not been investigated, nor has any study of these variants been performed among SCD patients in Africa. Aim: The aim of this study was to investigate the association of targeted single nucleotide polymorphisms (SNPs) in APOL1, MYH9 and HMOX1, as well as a 5' promoter dinucleotide repeat in HMOX1, with micro-albuminuria among SCD patients from Cameroon; and to compare the results to that from a cohort of non-SCD Cameroonian individuals affected by ESKD.
  • Thumbnail Image
    Item
    Open Access
    Bi-Allelic Novel Variants in CLIC5 Identified in a Cameroonian Multiplex Family with Non-Syndromic Hearing Impairment
    (2020-10-23) Wonkam-Tingang, Edmond; Schrauwen, Isabelle; Esoh, Kevin K; Bharadwaj, Thashi; Nouel-Saied, Liz M; Acharya, Anushree; Nasir, Abdul; Adadey, Samuel M; Mowla, Shaheen; Leal, Suzanne M; Wonkam, Ambroise
    DNA samples from five members of a multiplex non-consanguineous Cameroonian family, segregating prelingual and progressive autosomal recessive non-syndromic sensorineural hearing impairment, underwent whole exome sequencing. We identified novel bi-allelic compound heterozygous pathogenic variants in CLIC5. The variants identified, i.e., the missense [NM_016929.5:c.224T>C; p.(L75P)] and the splicing (NM_016929.5:c.63+1G>A), were validated using Sanger sequencing in all seven available family members and co-segregated with hearing impairment (HI) in the three hearing impaired family members. The three affected individuals were compound heterozygous for both variants, and all unaffected individuals were heterozygous for one of the two variants. Both variants were absent from the genome aggregation database (gnomAD), the Single Nucleotide Polymorphism Database (dbSNP), and the UK10K and Greater Middle East (GME) databases, as well as from 122 apparently healthy controls from Cameroon. We also did not identify these pathogenic variants in 118 unrelated sporadic cases of non-syndromic hearing impairment (NSHI) from Cameroon. In silico analysis showed that the missense variant CLIC5-p.(L75P) substitutes a highly conserved amino acid residue (leucine), and is expected to alter the stability, the structure, and the function of the CLIC5 protein, while the splicing variant CLIC5-(c.63+1G>A) is predicted to disrupt a consensus donor splice site and alter the splicing of the pre-mRNA. This study is the second report, worldwide, to describe CLIC5 involvement in human hearing impairment, and thus confirms CLIC5 as a novel non-syndromic hearing impairment gene that should be included in targeted diagnostic gene panels.
  • Thumbnail Image
    Item
    Open Access
    Biomedical research, a tool to address the health issues that affect African populations
    (BioMed Central Ltd, 2013) Peprah, Emmanuel; Wonkam, Ambroise
    Traditionally, biomedical research endeavors in low to middle resources countries have focused on communicable diseases. However, data collected over the past 20years by the World Health Organization (WHO) show a significant increase in the number of people suffering from non-communicable diseases (e.g. heart disease, diabetes, cancer and pulmonary diseases). Within the coming years, WHO predicts significant decreases in communicable diseases while non-communicable diseases are expected to double in low and middle income countries in sub-Saharan Africa. The predicted increase in the non-communicable diseases population could be economically burdensome for the basic healthcare infrastructure of countries that lack resources to address this emerging disease burden. Biomedical research could stimulate development of healthcare and biomedical infrastructure. If this development is sustainable, it provides an opportunity to alleviate the burden of both communicable and non-communicable diseases through diagnosis, prevention and treatment. In this paper, we discuss how research using biomedical technology, especially genomics, has produced data that enhances the understanding and treatment of both communicable and non-communicable diseases in sub-Saharan Africa. We further discuss how scientific development can provide opportunities to pursue research areas responsive to the African populations. We limit our discussion to biomedical research in the areas of genomics due to its substantial impact on the scientific community in recent years however, we also recognize that targeted investments in other scientific disciplines could also foster further development in African countries.
  • Thumbnail Image
    Item
    Open Access
    Chronic kidney disease in HIV populations: prevalence, risk factors and role of transforming growth factor beta (TGF-߀1) polymorphisms
    (2019) Ekrikpo, Udeme Ekpenyong; Okpechi, Ikechi; Kengne, Andre Pascal; Bello, Aminu; Dandara, Collet; Wonkam, Ambroise
    Background and purpose: With the advent of antiretroviral therapy, HIV-infected individuals now live longer and are at increased risk of chronic kidney disease (CKD). Also, recent studies indicate a genetic predisposition to CKD in the African HIV population. This work investigated the prevalence of CKD (and its correlates) in the global and local HIV population and proceeded to investigate the diagnostic utility of urinary transforming growth factor-beta-1 (TGF-β1) for CKD in the HIV population and determine the association between polymorphisms of TGF-β1 gene and prevalent CKD. Methods: A meta-analysis was performed to document the prevalence of CKD in the global HIV population. From the local HIV population in Nigeria, the prevalence of CKD and traditional risk factors for cardiovascular disease was determined. Using ELISA, TGF-β1 levels was assayed in the urine samples of HIV patients with or without CKD to investigate the ability of urinary TGF-β1 to diagnose early CKD. SNP genotyping of rs1800469, rs1800470, rs1800471, rs121918282 in TGF-β1, rs60910145 (APOL1), rs73885319 (APOL1), rs71785313 (APOL1) and rs743811 (HMOX1) was performed using predesigned TaqMan genotyping assays. Results: Using meta-analytic methods, the global pooled CKD prevalence was 6.4% (95%CI 5.2–7.7%) with MDRD, and 4.8% (2.9–7.1%) with CKD-EPI. Among the WHO regions, Africa had the highest MDRD-based prevalence, 7.9% (5.2-11.1%) with the West African subregion carrying the heaviest burden, 14.6% (9.9- 20.0%). Among the local HIV population, using the CKD-EPI equation, the prevalence of CKD was 13.4% (11.6- 15.4%). Hypertension prevalence was 26.7% (25.5-28.0%); diabetes 5.6% (4.5-6.7%); obesity 8.3% (7.6-9.1%) and dyslipidaemia 29.1% (26.1-32.1%). HIV-infected individuals with CKD had significantly higher levels of urinary TGF-β1-creatinine ratio (uTGFβ1Cr) after controlling for potential confounding factors in regression models. However, within the CKD-HIV group, uTGFβ1Cr reduced as CKD stage worsened. The presence of APOL1 genetic risk independently increased the risk of CKD (OR 2.54, 95% CI 1.44-4.51) in the HIV population while the TGF-β1 SNP, rs1800470, appeared to have a protective effect (OR 0.44 (95% CI 0.20-0.97). There was no significant association between HMOX1 SNPs and CKD occurrence. Conclusion: There is a high prevalence of CKD (and other cardiovascular risk factors) in the adult HIVpopulation. Urinary TGF-β1 may be useful in the non-invasive detection of early CKD in the HIV population. Genetic testing may be used to predict the risk of CKD in the HIV population.
  • Thumbnail Image
    Item
    Open Access
    The co-inheritance of alpha-thalassemia and sickle cell anemia is associated with better hematological indices and lower consultations rate in Cameroonian patients and could improve their survival
    (Public Library of Science, 2014) Rumaney, Maryam Bibi; Bitoungui, Valentina Josiane Ngo; Vorster, Anna Alvera; Ramesar, Raj; Kengne, Andre Pascal; Ngogang, Jeanne; Wonkam, Ambroise
    BACKGROUND: Co-inheritance of α-thalassemia was reported to be associated with a delayed age of disease onset among Cameroonian Sickle Cell Anemia (SCA) patients. The present study aimed to explore the correlation between α-thalassemia, hematological indices, and clinical events in these patients. Methods and FINDINGS: We studied 161 Cameroonian SCA patients and 103 controls (59.1% HbAA) with median ages of 17.5 and 23 years. RFLP-PCR was used to confirm SCA genotype and to describe haplotypes in the HBB-like genes cluster. Multiplex Gap-PCR was performed to investigate the 3.7 kb α-globin gene deletions. SNaPshot PCR, capillary electrophoresis and cycle sequencing were used for the genotyping of 10 SNPs in BCL11A , HMIP1/2 , OR51B5/6 and HBG loci, known to influence HbF levels. Generalised linear regression models adjusted for age, sex and SNPs genotypes was used to investigate effects of α-thalassemia on clinical and hematological indices. The median rate of vaso-occlusive painful crisis and hospitalisations was two and one per year, respectively. Stroke was reported in eight cases (7.4%). Benin haplotype was the most prevalent (66.3%; n = 208 chromosomes). Among patients, 37.3% ( n = 60) had at least one 3.7 kb deletion, compared to 10.9% ( n = 6) among HbAA controls (p<0.001). Among patients, the median RBC count increased with the number of 3.7 kb deletions [2.6, 3.0 and 3.4 million/dl, with no, one and two deletions (p = 0.01)]. The median MCV decreased with the number of 3.7 kb deletion [86, 80, and 68fl, with no, one and two deletions (p<0.0001)], as well as median WBC counts [13.2, 10.5 and 9.8×10 9 /L (p<0.0001. The co-inheritance of α-thalassemia was associated with lower consultations rate (p = 0.038). CONCLUSION: The co-inheritance of α-thalassemia and SCA is associated with improved hematological indices, and lower consultations rate in this group of patients. This could possibly improve their survival and explain the higher proportion of α-thalassemia among patients than controls.
  • Thumbnail Image
    Item
    Open Access
    Connexin Genes Variants Associated with Non-Syndromic Hearing Impairment: A Systematic Review of the Global Burden
    (2020-10-28) Adadey, Samuel Mawuli; Wonkam-Tingang, Edmond; Twumasi Aboagye, Elvis; Nayo-Gyan, Daniel Wonder; Boatemaa Ansong, Maame; Quaye, Osbourne; Awandare, Gordon A.; Wonkam, Ambroise
    Mutations in connexins are the most common causes of hearing impairment (HI) in many populations. Our aim was to review the global burden of pathogenic and likely pathogenic (PLP) variants in connexin genes associated with HI. We conducted a systematic review of the literature based on targeted inclusion/exclusion criteria of publications from 1997 to 2020. The databases used were PubMed, Scopus, Africa-Wide Information, and Web of Science. The protocol was registered on PROSPERO, the International Prospective Register of Systematic Reviews, with the registration number “CRD42020169697”. The data extracted were analyzed using Microsoft Excel and SPSS version 25 (IBM, Armonk, New York, United States). A total of 571 independent studies were retrieved and considered for data extraction with the majority of studies (47.8% (n = 289)) done in Asia. Targeted sequencing was found to be the most common technique used in investigating connexin gene mutations. We identified seven connexin genes that were associated with HI, and GJB2 (520/571 publications) was the most studied among the seven. Excluding PLP in GJB2, GJB6, and GJA1 the other connexin gene variants (thus GJB3, GJB4, GJC3, and GJC1 variants) had conflicting association with HI. Biallelic GJB2 PLP variants were the most common and widespread variants associated with non-syndromic hearing impairment (NSHI) in different global populations but absent in most African populations. The most common GJB2 alleles found to be predominant in specific populations include; p.Gly12ValfsTer2 in Europeans, North Africans, Brazilians, and Americans; p.V37I and p.L79Cfs in Asians; p.W24X in Indians; p.L56Rfs in Americans; and the founder mutation p.R143W in Africans from Ghana, or with putative Ghanaian ancestry. The present review suggests that only GJB2 and GJB3 are recognized and validated HI genes. The findings call for an extensive investigation of the other connexin genes in many populations to elucidate their contributions to HI, in order to improve gene-disease pair curations, globally.
  • Thumbnail Image
    Item
    Open Access
    Genetic aetiology of autosomal recessive non-syndromic hearing loss in sub-Saharan African patients: evaluation using targeted and whole exome sequencing
    (2019) Lebeko, Kamogelo; Wonkam, Ambroise; Dandara, Collet; Mowla, Shaheen
    Hearing Loss (HL) is one of the highest contributors to disability worldwide. The highest incidence of the disease is seen in developing countries, such as those in subSaharan Africa (SSA). Patients affected with disabling HL are reported to be more than 466 million worldwide. The causes of HL can either be environmental or genetic with each contributing about 50% towards all cases, in many settings. In developing countries, the environment might contribute more due to poor health services and infrastructure available to the population. In the absence of environmental causes, there is a genetic component at play, that is largely unknown in African populations. Up to 70% of HL of genetic origin are non-syndromic (NS). The mode of inheritance is recessive in nearly 77% of non-syndromic HL. Up to date, more than 100 genes have been associated with HL harbouring more than 1000 causative variants. In many populations of European and Asian descent, pathogenic variants in GJB2 (connexin gene 26) and GJB6 (connexin gene 30) are a major contributor to autosomal recessive non-syndromic hearing loss (ARNSHL). Comprehensive hearing health care programs should cover genetic causes by providing molecular testing, and genetic counselling, specifically SSA where genes and mutations causing HL remain largely unknown. The aim of this project was thus to uncover the genetic causes of HL among patients’ cohorts from Cameroon and South Africa. This was addressed by 1) sequencing common variants in the most relevant genes in other populations (GJB2 and GJB6), 2) using a targeted gene panel to resolve HL in 10 multiplex families from Cameroon presenting with ARNSHL and negative for GJB2 and GJB6 mutations screening, 3) screening novel variants found in known genes in a cohort of 82 singleplex HL cases from Cameroon and South Africa, and lastly, 4) using Whole Exome sequencing to explore the two unresolved multiplex cases with and subsequent findings confirmed by functional studies, and also screened in 80 singleplex HL cases. The following findings are reported: GJB6, GJA1 mutations screening and literature review No GJA1 or GJB6 mutation was not found in multiplex and simplex cases of HL in both Cameroonians and South Africans. The review of the literature confirms that the prevalence of GJB2- or GJB6-related NSHL is approximating to zero in most subSaharan African populations. Targeted Exome Sequencing (OtoSCOPE) The targeted genes, panel that included 116 genes, was able to resolve 7 of 9 families (77.8%) which were successfully sequenced, with one family failing to be sequenced. The causative variants identified in the 7 resolved families were : 1) compound heterozygous c.5806_5808delCTC and c.5880_5882delCTT in MYO7A; 2) compound heterozygous c.646T>A (p.Phe216Ile) and c.38G>A (p.Arg13His) in LOXHD1; 3) homozygous c.766-2A>G in OTOF; 4) a deletion and a complex copy number variation in STRC; 5) compound heterozygous c.1678G>A (p.Asp560Asn) and c.2007C>A(p.Asp669Glu) in SLC26A4; 6) Homozygous c.1996C>T(p.Arg666Stop) in MYO7A; 7) compound heterozygous c.6399C>A(p.Asp2133Glu) and c.2000T>C (p.Met667Thr) in CDH23. Five out of 12 variants were novel. Screening of these causative variants in known genes, in 82 singleplex HL cases from Cameroon and South Africa was unable to resolve any of the cases: the variants were in either heterozygous in low frequency or absent. Bioinformatic pathways exploration of SNP data of known HL genes revealed an extensive network within the HL genes, with 10 identified as important nodes, including MYO7A. Most HL genes were found to be involved in two biological processes which were sensory perception of mechanical stimulus (GO: 0050954, p= 1.430e-8) and sound (GO: 0007605, p = 1.246e-8). The molecular functions of variants found within these genes were found to mostly fall within the binding (GO: 0005488) and/or structural molecule activity (GO: 0005198). Whole Exome sequencing Whole exome sequencing was performed on four of the nine multiplex families: the two families that were unresolved by targeted panel sequencing, and two previously resolved families that were used as positive controls for the variant annotation and filtering pipeline. The results were the resolution of 3/4 families, including the two- positive control. The previously unresolved “family 8” was found to harbour a novel variant within the GRXCR2 gene, a gene only associated with HL once before. The c.251delC variant was revealed through in silico studies to cause a premature stop codon at position 116 due to its frameshift effect. The screening of this variant in our cohort of 80 singleplex cases revealed one other unrelated HL patient harbouring this causative variant. Due to the limited literature on the gene and its protein, in silico studies were used to show the predicted secondary structure folding of the protein as well as potential protein binding regions. Analysis showed that the predicted loss of a stable region of the protein as well as that of a putative binding domain could explain the pathogenic nature of the variant. In vitro studies showed that the variant hindered the detection of the protein by way of a DDK tag downstream in the plasmid. Additionally, GFP-Tagged GRXCR2 showed altered expression pattern in the variant when compared to the wildtype. In summary, our data has revealed the efficacy of using next generation sequencing tools in resolving HL among sub-Saharan African patients as opposed to the single candidate gene approach. In our quest, we have employed two widely used strategies, targeted panel and whole exome sequencing (WES), both of which have had great successes in various populations. The targeted approach was able to resolve 77.8% of our families but did not detect variants for two of the families revealing the presence of other variants harboured in rarely associated gene not captured or included on the panel. This prompted for the use of a more comprehensive approach such as WES. These results corroborated with those of two families previously resolved by targeted exome sequencing. Additionally, one of the previously unresolved family was now resolved. This showed that WES was sensitive enough to detect variants in known HL genes but comprehensive enough to detect variants in other regions of the exome which have not been associated with HL or rarely associated with HL. The benefit of WES also extends to the contribution of exomic data from patients of African descent as there is an underrepresentation of this group in exome repositories as well as genomic or SNP databases. To the best of our knowledge, this is the first study to use WES to resolve HL in patients of African descent. The other benefit of such a venture is the use of this data not only for patients in SSA but also those in the diaspora. In conclusion, we have successfully demonstrated the feasibility of using NGS tools in identifying causative variants in HL patients in SSA. Additionally, we have shown that WES is a more suitable approach to trying to resolve HL in Africa. Therefore, the data strongly support that genetic studies on families segregating HL in SSA could be the next frontier of HL genetic research, of global importance through discovering novel variants in known genes, and potentially novel genes. These studies will improve HL genetic diagnosis, retrospective counselling and testing, prevention and care including future prediction of treatment outcomes in sub-Saharan Africans, and in people of African descent.
  • Thumbnail Image
    Item
    Open Access
    Genetic investigation of South Africans with the Noonan Syndrome phenotype using targeted next generation sequencing
    (2017) Ngongang Tekendo, Cedrik; Wonkam, Ambroise; Esterhuizen, Alina
    Introduction: Noonan Syndrome (NS) is an autosomal dominant multisystem disorder, characterised by short stature, distinctive facial dysmorphism, cardiovascular abnormalities and developmental delay. Its estimated incidence is 1:1000 to 1:2500 live births. NS is caused by germline mutations in more than ten genes encoding proteins integral to the Ras/MAPK signaling pathway. Pathogenic variants in these genes account for 70-80% of NS cases. The clinical diagnosis of NS can be challenging in some cases, even when performed by experienced clinicians. The introduction of Next Generation Sequencing (NGS) technology in clinical practice in the Western world has tremendously facilitated the molecular diagnosis of RASopathies. Molecular testing for NS is not yet available in South Africa, nor has any study investigating NS from clinical and molecular perspectives been conducted in South Africans. Aim: The aim of this study was to investigate selected genes within a group of paediatric and adult patients with a clinical diagnosis of NS. Methods: This study was a cross-sectional descriptive study, including twenty-six familial and isolated NS patients recruited in Cape Town in the period January 2015-January 2017. Thorough phenotyping of each patient according to the international diagnostic criteria for NS was followed by targeted NGS, performed on leucocyte DNA samples from sixteen unrelated patients out of the twenty-six included. Sequencing involved all the exons and intron-exon boundaries of a predesigned panel of 14 genes, including A2ML1, BRAF, CBL, HRAS, KRAS, MAP2K1, MAP2K2, NRAS, PTPN11, RAF1, RIT1, SHOC2, SOS1 and SPRED1. Results: Of the 26 patients included, 50% had a family history suggestive of NS. The median age at diagnosis was4.5 years (range: 1month-51years). Individuals of mixed-race ancestry were most represented (53.8%), followed by black Africans (30.8%). The clinical features identified were consistent with those reported in other populations. Compared to other series, our cohort revealed a lower frequency of Pulmonary Valve Stenosis (34.6%) and a less severe developmental phenotype. Variants predicted pathogenic were detected in 7(43.7%) DNA samples out of the 16 analysed. The genes involved were CBL in three cases (42.8%), PTPN11and MAP2K1in two cases (28.6%, for each gene). Surprisingly, the proportion of CBL variants was relatively high compared to those in the literature. Genotype-phenotype correlations showed that clinical features of NS were more typical in patients with pathogenic variants in MAP2K1, and less in those with variants in CBL. Conclusion: This is the first clinical and molecular study in South Africans with the NS phenotype. The phenotype of affected individuals with NS in South Africa is globally similar to that reported in the literature. Therefore, the use of international diagnostic criteria can effectively enable the clinical diagnosis of NS in most South African patients. These preliminary data suggest that the distribution of pathogenic variants in NS genes in South Africans may be different from that reported in other populations. Finally, this study demonstrates that Targeted NGS can be successfully applied to the molecular diagnosis of NS and related conditions in South Africa, and should be implemented in clinical practice.
  • Thumbnail Image
    Item
    Open Access
    Genetic variation in toll like receptors 2, 7, 9 and interleukin-6 is associated with cytomegalovirus infection in late pregnancy
    (2020-05-25) Mhandire, Doreen Z; Mhandire, Kudakwashe; Magadze, Mulalo; Wonkam, Ambroise; Kengne, Andre P; Dandara, Collet
    Background Maternal cytomegalovirus (CMV) infection and/or reactivation in pregnancy is associated with a myriad of adverse infant outcomes. However, the role of host genetic polymorphisms in modulating maternal CMV status is inconclusive. This study investigated the possible association of single nucleotide polymorphisms in toll-like receptor (TLR) and cytokine genes with maternal plasma CMV DNA status in black Zimbabweans. Methods In a cross-sectional study, 110 women in late gestation who included 36 CMV infected cases and 74 CMV uninfected, age and HIV status matched controls were enrolled. Twenty single nucleotide polymorphisms in 10 genes which code for proteins involved in immunity against CMV were genotyped using Iplex GOLD SNP genotyping protocol on the Agena MassARRAY® system. Statistical analyses were performed using Stata SE and the ‘Genetics’ and ‘SNPassoc’ packages of the statistical package R. Results The TLR7 rs179008A > T (p < 0.001) polymorphism was associated while the TLR9 rs352139T > C (p = 0.049) polymorphism was on the borderline for association with CMV positive (CMV+) status. In contrast, the interleukin (IL)-6 rs10499563T > C (p < 0.001) and TLR2 rs1816702C > T (p = 0.001) polymorphisms were associated with CMV negative (CMV-) status. Furthermore, allele frequencies of SNPs in TLR2, TLR4, TLR9, TLR7, IL-6, IL-10, IL-28B, IL-1A and interferon AR1 (IFNAR1) genes are being reported here for the first time in a Zimbabwean population. The allele frequencies in the Zimbabwean population are generally comparable to other African populations but different when compared to European and Asian populations. Conclusions Toll-like receptor and interleukin genetic polymorphisms influence CMV status in late gestation among black Zimbabweans. This is attributable to possible modulation of immune responses to CMV reactivation in a population previously exposed to CMV infection.
  • Thumbnail Image
    Item
    Open Access
    Genetics of hearing impairment and peripheral neuropathy in Mali
    (2023) Yalcouye, Abdoulaye; Wonkam, Ambroise; Chimusa Emile
    Background Hearing impairment (HI), the most common sensory disturbance, affects about 1 in 1000 living newborns globally. Its incidence is reported higher in sub-Saharan African (SSA) populations. HI is caused by environmental and genetics factors. In many developing countries, environmental factors are reported to be the most prevalent aetiologies while genetic causes are predominant in the developed countries. Over 50% of congenital HI has a genetic origin with more than 120 genes identified to date. Despite this large number of known genes, only GJB2 (OMIM: 121011) and GJB6 (OMIM: 604418) are systematically studied in SSA populations for which the prevalence of HI-causal variants is insignificant. Charcot-Marie-Tooth disease (CMT), is the most common inherited peripheral neuropathy (IPN) with a high clinical and genetic heterogeneity and over 100 genes are related to CMT, mostly in populations of Caucasian ancestry. Yet, despite being described more than 130 years ago, there remains a paucity of information on its global prevalence and genetic epidemiology due largely to challenges in diagnosis, especially in countries with limited resources. Over 90% of CMT are caused by mutations in PMP22 (OMIM: 601097), GJB1 (OMIM: 304040), MFN2 (OMIM: 608507), MPZ (OMIM: 159440) genes. HI is the common audiological symptom associated with CMT and is caused by several genes including PMP22 and GJB1. HI and IPN are inherited in autosomal (dominant and recessive), X-linked, and mitochondrial transmission. However, the genetic epidemiology of these diseases are largely unknown in Africa, and have not been investigated in Mali where consanguineous marriage is a common practice that may increase recessive conditions.
  • Thumbnail Image
    Item
    Open Access
    Genomic medicine in Africa: promise, problems and prospects
    (BioMed Central Ltd, 2014) Wonkam, Ambroise; Mayosi, Bongani
    Remarkable progress has been made in using genomic information to determine how genes are regulated, and how they interact with each other and with the environment to control complex biochemical functions of living organisms in health and disease [1]. This information will have major benefits for the prevention, diagnosis and management of many diseases, including communicable and genetic diseases. In Africa, where infectious diseases are highly prevalent, research on pathogen genomes has enhanced our understanding of disease transmission, virulence mechanisms and avoidance of host defenses [2]. It is anticipated that this information will enable the development of new diagnostic tests, vaccines and therapeutic agents; it is also likely to lead to new approaches for vector control, and reveal why individuals and populations vary in their susceptibility to infectious diseases [1].
  • No Thumbnail Available
    Item
    Open Access
    Genomics of sickle cell disease and fetal hemoglobin in African populations
    (2024) Esoh, Kum Kevin; Wonkam, Ambroise
    Background More than 300,000 babies are born with sickle cell disease (SCD) each year. About 79% of these births occurs in sub-Saharan Africa where the sickle variant is known to have originated in the genetic background of the ancestors of Agriculturalist populations. Although the variant is highly lethal, the protection it confers against severe malaria in its heterozygous form has resulted in its persistence in sub-Saharan Africa where malaria is endemic. Without intervention, 50–90% of affected children in many sub-Saharan African countries die before their fifth birthday. The search for a definitive cure or effective disease-modifying therapy is therefore an imperative. Fetal hemoglobin (HbF) has long been recognized to ameliorate SCD severity whereby patients harboring natural genetic variations that lead to the persistence of high HbF levels in their blood tend to live longer with fewer complications. The HbF quantitative trait is highly heritable (89%), and is therefore the focus of enormous research for therapeutic purposes. Genetic polymorphisms influencing HbF level have been identified in three major loci; BCL11A, HBS1LMYB, and HBG2. However, these loci jointly explain less than 30% of HbF variability in African sickle cell anemia (SCA) patients as compared to ~50% in African Americans and non-anemic Europeans. Genome-wide association studies have been employed to replicate two of the three major loci (BCL11A and HBS1L-MYB) in African SCA patients, as well as to identify new loci including BACH2 involving a meta-analysis of African Americans and Tanzanians, SLC28A3, TICRR, and PIEZO2 in Nigerians, and FRMPD4 in Tanzanians. While BCL11A and HBS1L-MYB have been replicated in Cameroonian SCD patients through candidate genotyping studies, there has yet to be a genome-wide investigation. Moreover, the long survival of SCA patients in Africa despite a higher disease severity and mortality in the region hints at the enrichment of African genomes with ‘protective' polymorphisms potentially impacting the level of HbF, the strongest modifier of SCD severity. A better understanding of the genetic architecture of HbF in African SCA patients is therefore needed to foster research into potentially novel sickle cell disease therapeutic targets. Aims and Methods This thesis project aimed to: 1) present an in-depth description of the evolutionary history of the sickle cell mutation and its implication for global genetic medicine through a synthesis of publicly available data. This included updating and summarising the global georeferenced databases of the sickle gene and the HBB gene cluster haplotypes, systematically and critically evaluating the age and place of origin of the sickle cell mutation by incorporating information about malaria with which its evolution is highly intertwined, summarising bibliographic information on the genetic modifiers of SCD severity, and, importantly, examining other gene variants that co-occur with the sickle gene in sub-Saharan Africa that might hint at possible co-evolution and effect on SCD severity; 2) provide a comprehensive overview of SCD in Sub-Saharan Africa, bringing out transferable strategies and recommendations for prevention and care, through bibliographic searches; and 3) to investigate the missing heritability of HbF in SCA patients of African ancestry from Cameroon, Tanzanian, and the USA through a multiple imputation panel and genome-wide association approach, with fine-mapping and functional analysis. Briefly, the performance of different reference haplotype panels on genotype imputation accuracy for African SCA populations from Cameroon and Tanzania was assessed. Genome-wide association analyses for the two populations using all the imputation panels was performed, and then meta-analyses of the two populations, as well as with summary statistics from the USA-based cohorts. Statistical fine mapping and extensive in silico functional analyses were next performed to determine the functional relevance of significant associations, while extensive haplotype structure analysis was performed to illuminate the reason for substantial heterogeneity in association signals across different populations of the same ancestry. Finally, gene-based and gene set enrichment analyses were undertaken to identify additional significant loci and significantly enriched pathways, while heritability analysis was performed to further appreciate the observations of multiple significant signals and to better understand the genetic architecture of HbF in African SCA patients. Results Evolutionary history of sickle cell mutation In this first part, we successfully updated the global georeferenced databases of the sickle gene and the HBB gene cluster haplotypes. We showed that changes in population dynamics, contributed by migration and gene flow, might be introducing some HBB haplotypes in regions where they were previously absent, reflecting changes in regional SCD severity. Through our systematic and critical evaluation of the origin of the sickle cell mutation, we identified limitations to the models that have been used to estimate the age of the mutation, and we determined that the mutation is likely older than its currently held age of 22,000 years. Using data on the emergence of malaria, we determined that the mutation is most likely to have originated somewhere in West-Central Africa. Importantly, we showed overlapping distribution of the sickle gene and other gene variants that are under natural selection in sub-Saharan Africa. Data suggest that some of these gene variants impact SCD severity, while others have known modifying effects on the disease severity. Overview of sickle cell disease in sub-Saharan Africa We provided and overview of SCD in sub-Saharan Africa with transferable strategies for prevention and care as part of the Lancet Haematology's 2021 series on hematological care priorities in sub-Saharan Africa. We touched on aspects of SCD such as epidemiology, burden, mortality and life expectancy, hematological parameters, diagnosis, pathophysiology, biological and genetic modifiers of severity, management, environmental determinants, and psychosocial effects. We also presented challenges and proposed recommendations for SCD research in subSaharan Africa. Impact of reference haplotype panels on genotype imputation in African sickle cell anemia populations To use the genomics of HbF to search for other, perhaps more effective, targets of gene editing for better management and perhaps cure of SCD, we first assessed the impact of imputing missing genotypes into genome-wide single nucleotide polymorphism (SNP) data using different reference haplotype panels. We used six different panels including one which we created ourselves from whole genome sequencing data of fifty Cameroonians. The key observations included: i) different imputation performance for different African populations; ii) different imputation performance among different imputation panels within each African population, indicating that one variant can be imputed with vastly different accuracies across different panels, reflecting differences in haplotype structures across the panels resulting from different tagging schemes. This underscoresthe complementary use of the panels, with an expectation of different patterns of association (panel-specific significant signals). Genome-wide association analysis, statistical and functional fine mapping As expected from our assessment of imputation performance, we observed multiple panelspecific significant signals. We replicated the major known loci including BCL11A and HBS1L-MYB, and uncovered fourteen novel loci. The most significant of the novel loci, FLT1, which was observed in Cameroonians and replicated in a meta-analysis with Tanzanians, has known role in hematopoiesis. Fine-mapping and in silico functional analyses suggest an important role in HbF induction. Gene-based, gene set enrichment, and heritability analyses Gene-based analysis confirmed significant signals in the three major HbF-influencing loci, BCL11A, HBS1L-MYB, and HBG2. Gene set enrichment analysis revealed an overwhelming enrichment of hematopoiesis related pathways, as well as hemoglobin as the major enriched biological component, while blood traits were the most enriched phenotypes. Consistent with these, we estimated HbF heritability in a joint cohort of Cameroonian and Tanzanian SCA patients at 94% suggesting an enrichment of these populations with HbF-influencing loci in a way that has probably been underappreciated, and that might be better revealed through whole-genome sequencing. Conclusion and perspectives Our study presented data with overwhelmingly support for a single African origin of the sickle cell mutation, with opportunity for further research on determining the true age of the mutation. Tracking the movement of the mutation through the distribution of the HBB gene cluster haplotypes highlighted changing population dynamics that are important for public health. Calling attention to gene variants whose distribution in sub-Saharan Africa overlaps with the sickle gene is important because the co-occurrence could mean co-evolution which might suggest an impact on SCD severity. Therefore, further evolutionary genetic studies are warranted to understand the interactions of these gene variants and the sickle gene. We equally showed that progress in implementing newborn screening and comprehensive care in some sub-Saharan African countries has been encouraging. Early diagnosis and family education on management can reduce morbidity, while immunisation and hydroxyurea therapy initiated in affected children as young as 9 months old can greatly improve quality and quantity of life. Research in sub-Saharan Africa is urgently needed to establish the exact prevalence, mortality, and morbidity, environmental and genetic factors affecting clinical complications, and life expectancy of patients with sickle cell disease, to facilitate the design of future risk models and to investigate novel routes for therapeutic options with the ultimate aim of improving the clinical outcomes of patients with SCD in all parts of the world. Finally, our discovery of new genes that are associated with blood levels of HbF which is the strongest modifier of SCD severity and the target of gene editing means that our work has tremendous potential towards discovery of novel SCD therapeutic targets, but also in improving our understanding of the genetic architecture of HbF in understudied African populations.
  • Thumbnail Image
    Item
    Open Access
    GJB2 Is a Major Cause of Non-Syndromic Hearing Impairment in Senegal
    (2022-05-23) Dia, Yacouba; Adadey, Samuel Mawuli; Diop, Jean Pascal Demba; Aboagye, Elvis Twumasi; Ba, Seydi Abdoul; De Kock, Carmen; Ly, Cheikh Ahmed Tidjane; Oluwale, Oluwafemi Gabriel; Sène, Andrea Regina Gnilane; Sarr, Pierre Diaga; Diallo, Bay Karim; Diallo, Rokhaya Ndiaye; Wonkam, Ambroise
    The prevalence of GJB2-related (MIM: 121011) congenital non-syndromic hearing impairment (NSHI) accounts for close to 50% in populations of Asian and European ancestry. However, in sub-Saharan Africa, except for Ghana, previous data showed that the prevalence of GJB2-associated NSHI is close to zero. To investigate the contribution of GJB2 mutations in autosomal recessive NSHI in Senegal, we screened 129 affected and 143 unaffected individuals from 44 multiplex families, 9 sporadic cases, and 148 hearing controls with no personal or family history of hearing impairment, by targeted gene sequencing. We identified three pathogenic GJB2 variants in 34% (n = 15/44) of multiplex families, of which 80% (n = 12/15) were consanguineous. The most common variant, GJB2: c.94C>T: p.(Arg32Cys), accounted for 27.3% (n = 12/44) of familial cases. We also identified the previously reported “Ghanaian” founder variant, GJB2: c.427C>T: p.(Arg143Trp), in four multiplex Senegalese families. Relatively high allele frequencies of c.94C>T. and c.427C>T variants were observed among the screened hearing controls: 1% (n = 2/148 ∗ 2), and 2% (n = 4/148 ∗ 2), respectively. No GJB6-D13S18 deletion was identified in any of the hearing-impaired participants. The data suggest that GJB2: c.94C>T: p.(Arg32Cys) should be routinely tested in NSHI in Senegal.
  • Thumbnail Image
    Item
    Open Access
    Heterozygous p.Asp50Asn mutation in the GJB2 gene in two Cameroonian patients with keratitis-ichthyosis-deafness (KID) syndrome
    (BioMed Central Ltd, 2013) Wonkam, Ambroise; Noubiap, Jean; Bosch, Jason; Dandara, Collet; Toure, Genevieve
    BACKGROUND: Keratitis-Ichthyosis-Deafness (KID) syndrome (OMIM 148210) is a congenital ectodermal defect that consists of an atypical ichthyosiform erythroderma associated with congenital sensorineural deafness. KID appears to be genetically heterogeneous and most cases are caused by GJB2 mutations. Mutations in African patients have been rarely described.CASE PRESENTATION:We report on two unrelated Cameroonian individuals affected with sporadic KID, presenting with the classic phenotypic triad. The two patients were heterozygous for the most frequent p.Asp50Asn mutation. This first report in patients from sub-Saharan African origin supports the hypothesis that the occurrence of KID due to p.Asp50Asn mutation in GJB2 seems not to be population specific. CONCLUSIONS: Our finding has implication in medical genetic practice, specifically in the molecular diagnosis of KID in Africans. These cases also reveal and emphasize the urgent need to develop appropriate policies to care for patients with rare/orphan diseases in Sub-Saharan Africa, as many of these cases become more and more recognizable.
  • Thumbnail Image
    Item
    Open Access
    Identifying Genes and Novel Variants Involved in Nonsyndromic Hearing Impairment, and Assessment of the Psychosocial Burden of Hearing Impairment in Cameroon
    (2021) Wonkam, Tingang Edmond; Chimusa, Emile R; Wonkam, Ambroise
    Background Hearing impairment (HI) is the most common sensory disability and occurs in about 1 per 1000 live births in high-income countries, with a much higher incidence of up to 6 per 1000 live births in sub-Saharan Africa (SSA). HI can be due to environmental or genetic causes, and in many cases, it is not possible to establish a definite aetiology. Hereditary HI contributes to 30% to 50% of HI cases in SSA. Hereditary HI can be syndromic or non-syndromic, depending on whether it is associated with additional abnormalities in other organs or not. Non-syndromic HI (NSHI) accounts for 70% of hereditary hearing loss, and is genetically highly heterogeneous, with approximately 170 loci and 121 genes identified to date. Studies in European and Asian populations have identified pathogenic variants in GJB2 (MIM: 121011), and GJB6 (MIM: 604418) genes as the major contributors to autosomal recessive NSHI (ARNSHI). The genetic aetiology of HI in Cameroon is unclear, as previous studies have found no contribution of GJB2 and GJB6 genes to NSHI in Cameroon. However, patients included in those studies consisted of both familial and isolated cases, therefore, underlying environmental/multifactorial causes in some cases cannot be excluded (especially for the isolated cases). Six loci for X-linked HI have been described to date, including DFNX3 (Xp21.2), where DMD is located. Variants in DMD in humans are known to be responsible for Duchenne muscular dystrophy (DMD; MIM: 310200), and Becker muscular dystrophy (BMD; MIM: 300376), an Xlinked recessive disorder. Previous studies have demonstrated that mdx mice, (an animal knockout model for DMD), have an increased threshold for hearing when compared to wildtype mice. However, the contribution of DMD to HI in humans has not been extensively studied. Besides, most of the previous studies on DMD were conducted in Caucasians, Asians, and Arabs; therefore, little is known about the features of this condition in Africans. Parents of children with HI tend to face challenges of parenting especially in terms of communication and social interaction. In Africa, parent's perceived causes of deafness vary from environmental factors to mysterious (“evil forces”) or superstitious beliefs. Also, the attitude of the society towards people with HI does not encourage their participation and involvement in the community, as they face overt discrimination. Aim and methods The aim of this project was to examine the genetic aetiologies of HI in the Cameroonian population, and undercover the challenges faced by persons with HI in Cameroon and their understanding of the causes of HI. This was addressed by 1) Establishing the current status of knowledge on HI in Africa (in terms of prevalence, aetiologies, and genetics aspects) with a particular focus on Cameroon, and assessing the contribution of connexin genes to HI in humans at a global level, through systematic literature reviews; 2) Revisiting the contribution of GJB2 and GJB6 genes to NSHI in 29 multiplex Cameroonian families with NSHI and with strong evidence of non-environmental causes, through targeted gene sequencing and specific multiplex polymerase chain reaction (PCR); 3) Using multiplex ligand-dependent probe amplification (MLPA) technique to investigate the most common variants associated with DMD in Cameroon and assess their possible implication in HI in humans; 4) Performing whole exome sequencing (WES) on 2 Cameroonian multiplex families with NSHI and who tested negative for pathogenic variants in GJB2 and GJB6, to identify the underlying causative genes; 5) Performing in-depth interviews to gain an understanding of the challenges faced by people with HI in Cameroon, their understanding of the causes of hearing impairment (HI), and how challenges could be remedied to improve the quality of life of persons with HI. Results Literature reviews Our first systematic review showed that HI is a public health issue in Cameroon, especially in the elder population where the prevalence of HI is 14.8% in people aged 50 years and more. Environmental factors, including meningitis, impacted wax, and age-related disorders are the leading aetiologies of HI in Cameroon as in many other SSA countries, contributing 52.6% to 62.2% of HI cases. Hereditary HI comprises 0.8% to 14.8% of all cases in Cameroon, and in 32.6% to 37% of HI cases, the origin remains unknown. This contrasts with findings from highincome countries where hereditary HI constitutes the main aetiology of HI, contributing to approximately 50% of cases. NSHI is the most frequent clinical entity and accounts for 86.1% to 92.5% of cases of hereditary HI in the Cameroonian population. No pathogenic variant was described in GJB6 gene, and the prevalence of pathogenic variants in GJB2 ranged from 0% to 0.5%. The prevalence of pathogenic variants in other known NSHI genes was with type 2 Waardenburg syndrome, and three cases of type 2 Usher syndrome were identified in one family. By direct gene sequencing of the coding region of GJB2, no variants were found in any of the 29 families with NSHI. Additionally, through a specific multiplex PCR, the GJB6- D3S1830 deletion which contributes to 9.7% of NSHI cases in Europeans was not identified in any of the patients with HI. Subsequently, a total of 17 males with DMD from 14 families were recruited, aged 14 ± 5.1 (8–23) years. The mean age at onset of symptoms was 4.6 ± 1.5 years, and the mean age at diagnosis was 12.1 ± 5.2 years. Proximal muscle weakness was noted in all patients and calf hypertrophy in the large majority of them (88.2%; 15/17). Flexion contractures were particularly frequent on the ankle (85.7%; 12/14). Wasting of the shoulder girdle and thigh muscles was present in 50% (6/12) and 46.2% (6/13) of patients, respectively. No patient presented with HI. The MLPA found that deletions of at least one exon in DMD occurred in 45.5% of patients (5/11), while duplications were observed in 27.3% (3/11). Both variant types were clustered between exons 45 and 50, and the proportion of de novo variant was estimated at 18.2% (2/11). Whole exome sequencing We submitted DNA samples from five members of a multiplex non-consanguineous Cameroonian family segregating prelingual and progressive ARNSHI for WES. We identified novel bi-allelic compound heterozygous pathogenic variants in CLIC5 (MIM: 607293). The variants identified, i.e. the missense [NM_016929.5:c.224T>C; p.(Leu75Pro)] and the splicing (NM_016929.5:c.63+1G>A), were validated using Sanger sequencing in all seven available family members and co-segregated with HI in the three family members with HI. The three affected individuals were compound heterozygous for both variants, and all unaffected individuals were heterozygous for one of the two variants. Both variants classify as pathogenic by the American College of Medical Genetics (ACMG) guidelines for classification of variants and are absent from the genome aggregation database (gnomAD), UK10K, Greater Middle East (GME) database, and the Single Nucleotide Polymorphism Database (dbSNP), as well in 122 healthy controls from Cameroon. We also did not identify these pathogenic variants in 118 unrelated sporadic cases of NSHI from Cameroon. A second multiplex family was also screened through the use of WES, followed by direct Sanger sequencing in additional patients and control participants. We identified a heterozygous novel missense variant [NM_001174116.2:c.918G>T; p.(Gln306His)] in DMXL2 (MIM:612186) which was transmitted in an autosomal dominant manner, and co-segregates with congenital/prelingual profound to total non-syndromic sensorineural HI in a family from Cameroon. The described family showed a variable expressivity of the HI phenotype. The p.(Gln306His) variant which substitutes a highly conserved glutamine residue is predicted deleterious by various bioinformatics tools and is absent from several genome databases including genome aggregation database (gnomAD), and trans-omics for precision medicine (TOPMed) database. This variant was neither found in 121 healthy controls without personal or family history of HI, nor 112 sporadic cases of NSHI from Cameroon. Our study identified novel variants in CLIC5 and DMXL2 in two Cameroonian families, and provided only the second report of variants in these genes worldwide; thus, strengthening the case for these two genes as candidate genes for NSHI in humans. The psychosocial burden of HI We performed in-depth interviews with 10 HI professionals (healthcare workers, and educationists), and 10 persons affected by HI (persons with HI, and caregivers). The results show that in this study population, the cause of HI is attributed to a variety of causes, including genetics, environmental factors, and a spiritual curse. There were reported cases of stigma and discrimination with persons with HI in the Cameroonian population sometimes seen as having a “mental disorder”. Our participants also highlighted the difficulty that persons with HI have in accessing the necessary education and healthcare services, and suggested the need for policymakers and researchers to develop strategies to improve the social integration of persons with HI and their access to basic social services. This includes 1) Increased awareness amongst the general population, 2) the establishment of more special schools, and 3) building and equipping facilities for proper management of HI. Conclusions Our project confirms that variants in GJB2 and GJB6 genes do not contribute significantly to NSHI in the Cameroonian population. Also, variants in DMD that were shown to be associated with an increased hearing threshold in mice, do not seem to be implicated in HI in Cameroon, neither in previous human studies (although they did not objectively assess hearing using standardized testing methods). Despite the first symptoms of DMD occurring in infancy, the diagnosis is frequently made later in adolescence, indicating an underestimation of the number of cases of DMD in Cameroon. Future screening of deletions and duplications in patients from Cameroon should focus on the distal part of the DMD gene. Subsequently, this study successfully identified the candidate genes in two Cameroonian multiplex families with NSHI through the use of WES, and thus highlights the efficacy of next-generation sequencing techniques in resolving HI cases in Cameroonians and in cases where no pathogenic variants are found in common HI-genes. Additionally, our project which confirms that CLIC5 and DMXL2 genes are associated with HI in humans advocate for the inclusion of these two genes in diagnostic gene panels for NSHI in clinical settings. Last, this study shows the difficult social interaction and access to proper management faced by persons with HI in Cameroon, and highlights the need to educate populations on the causes of HI for a better acceptance of persons with HI in the Cameroonian society.
  • Thumbnail Image
    Item
    Open Access
    Implementation science research for the scale-up of evidence-based interventions for sickle cell disease in africa: a commentary
    (2021-02-17) Gyamfi, Joyce; Ojo, Temitope; Iwelunmor, Juliet; Ogedegbe, Gbenga; Ryan, Nessa; Diawara, Amy; Nnodu, Obiageli; Wonkam, Ambroise; Royal, Charmaine; Peprah, Emmanuel
    Background The burden of sickle cell disease (SCD) is greatest among African nations. Effective scalability of evidence-based interventions (e.g., newborn screening, health education, prophylaxis for infection, optimal nutrition and hydration, hydroxyurea therapy, blood transfusions, and transcranial Doppler (TCD) screening) is urgently needed particularly in these settings for disease management. However, Africa is constrained by limited resources and the lack of capacity to conduct implementation science research for proper understanding of context, and assessment of barriers and facilitators to the uptake and scalability of evidence-based interventions (EBI) for SCD management. Main Body We outline implementation science approaches to embed EBI for SCD within the African context and highlight key implementation research programs for SCD management. Building implementation research capacity will meet the major need of developing effective life-long and accessible locally-tailored interventions for patients with SCD in Africa. Conclusion This commentary communicates the importance of the application of implementation science methodology to scale-up evidence-based interventions for the management of SCD in order to reduce pain, prevent other morbidities and premature death experienced by people with SCD in Africa, and improve their overall quality of life.
  • Thumbnail Image
    Item
    Open Access
    Knowledge and experiences of parents with children affected by Sickle Cell Disease in Cape Town
    (2015) Van Niekerk, Katryn; Wonkam, Ambroise; de Vries, Jantina
    Sickle Cell Disease (SCD) is an autosomal recessively inherited blood disorder that leads to a debilitating systemic illness. Although the disease was initially found predominantly in tropical and subtropical regions, SCD has now become a global health problem, due to migration of people from various countries with a high burden thereof. Consequently, the incidence of SCD in South Africa has increased dramatically over the last decade. This study, which constitutes a minor dissertation in fulfilment of an MSc (Med) Genetic Counselling degree, aimed to explore the knowledge and understanding of SCD among parents of affected children in Cape Town as well as identify burdens associated with caring for a child with SCD. Furthermore, the study assessed opportunities to improve genetic counselling services available to parents and explored their attitude to preventive policies. A phenomenological approach was used to conduct this research. Seventeen semi-structured interviews were conducted with the biological parent of a child attending the Red Cross War Memorial Children's Hospital Haematology Clinic. Participants were selected using both purposive and convenience sampling methods. Data collected during these interviews were analysed using thematic content analysis. Themes and relevant sub-themes were identified and grouped into three categories: knowledge and understanding; experiences and burdens; and attitude toward preventative policies. While the majority of participants had some knowledge of SCD, several misconceptions were discovered, often relating to participants' prior knowledge of the disease. A number of burdens experienced by participants were revealed, with both practical and psychosocial implications. Finally, it was found that the majority of participants supported all methods of screening for SCD, regardless of whether they would make use of the screening services themselves. Findings of this study provide valuable insights on the subject of experiences of parents of children affected with SCD as well as the potential role of genetic counselling services. This study contributes towards improving understanding and subsequent services provided to individuals raising a child affected with Sickle Cell Disease.
  • Thumbnail Image
    Item
    Open Access
    Low hepatitis B vaccine uptake among surgical residents in Cameroon
    (2014-03-14) Noubiap, Jean J N; Nansseu, Jobert R N; Kengne, Karen K; Wonkam, Ambroise; Wiysonge, Charles S
    Abstract Background Hepatitis B virus (HBV) infection is one of the most serious occupational hazards faced by healthcare workers. Surgical personnel are particularly at risk. HBV infection is preventable by vaccination, but no previous study has assessed HBV vaccination coverage among healthcare workers in Cameroon. We assessed knowledge of risk factors of HBV infection, awareness of HBV vaccine, and vaccination status of surgical residents in Cameroon. Methods A structured pretested questionnaire was administered to 49 of the 70 surgical residents in Cameroon during the 2011–2012 academic year. Results Since the beginning of their residency program, 28 (57.1%) had had at least one accidental exposure to blood, with a median of 2 (range 1 to 25) exposures. Most of them had a good knowledge of risk factors for HBV infection. Although 98.0% (n = 48) were aware of the HBV vaccine, and 89.8% (n = 44) knew that they were at high risk of infection, only 24.5% (n = 12) had received a full course of at least three doses of the vaccine. In addition, only 33.3% (4/12) underwent post-vaccination testing to confirm a good immunological response (and thus effective protection against HBV infection). Among the 53.1% (n = 28) who had never had any dose of HBV vaccine, the main reasons for not being vaccinated were lack of time (38.5%), lack of money to pay for vaccine (23.1%), and lack of sufficient information on the vaccine (19.2%). Only 20.4% (n = 10) had been sensitized by their training institutions about the importance of HBV vaccination. Conclusion There is a low HBV vaccine uptake among surgical residents in Cameroon. As part of occupational safety measures, complete HBV vaccination should be strongly recommended and offered to surgical trainees before the beginning of their training program.