Common genes for non-syndromic deafness are uncommon in sub-Saharan Africa: A report from Nigeria

Abstract

INTRODUCTION Little is known about the molecular epidemiology of deafness in sub-Saharan Africa (SSA). Even in Nigeria, the most populous African nation, no genetic studies of deafness have been conducted. This pioneering work aims at investigating the frequencies of gene mutations relatively common in other parts of the world (i.e. those in GJB2, GJB6, and mitochondrial DNA) among subjects from Nigeria with hearing loss (HL) with no evidence of acquired pathology or syndromic findings. In addition, we review the literature on the genetics of deafness in SSA. METHOD We evaluated 81 unrelated deaf probands from the Yoruba tribe residing in Ibadan, a suburban city in Nigeria, for the etiology of their deafness. Subjects underwent genetic testing if their history was negative for an environmental cause and physical examination did not find evidence of a syndrome. Both exons of GJB2 and mitochondrial DNA flanking the 1555A>G mutation were PCR-amplified followed by Sanger sequencing. GJB6 deletions were screened via quantitative PCR. RESULT We identified 44 probands who had nonsyndromic deafness with no environmental cause. The age at study time ranged between 8 months and 45 years (mean=24 years) and age at onset was congenital or prelingual (<age 2 years) in 37 (84%) probands and postlingual in 7 (16%) probands. Among these, 35 probands were the only affected members of their families (simplex cases), while there were at least two affected family members in 9 cases (multiplex). Molecular analyses did not show a pathogenic variant in any one of the 44 probands studied. CONCLUSION GJB2, GJB6 and mitochondrial DNA 1555A>G mutations were not found among this initial cohort of the deaf in Nigeria. This makes imperative the search for other genes in the etiology of HL in this population.

Hearing Impairment Overview in Africa: the Case of Cameroon

“…Apart from the Ghanaian population, where the GJB2 founder mutation p.R143W (c.427C>T) was shown to be highly prevalent [17] and implicated in approximately 25% of familial cases and 8% of isolated cases of HI [18], our study is consistent with previous reports in other populations of African descent [68,69]. Mutations in GJB6, including the 342-kb deletion, GJB6-D13S1830, were not reported in cohorts of 182, 44 and 401 probands from South Africa, Nigeria and Ghana, respectively [18,69,70]. As in the Cameroonian population, disease-causing mutations in GJB2 are also less prevalent or absent in populations from Kenya, Sudan, Uganda, Nigeria, Mauritania and South Africa [5,33,[69][70][71][72].…”

“…Mutations in GJB6, including the 342-kb deletion, GJB6-D13S1830, were not reported in cohorts of 182, 44 and 401 probands from South Africa, Nigeria and Ghana, respectively [18,69,70]. As in the Cameroonian population, disease-causing mutations in GJB2 are also less prevalent or absent in populations from Kenya, Sudan, Uganda, Nigeria, Mauritania and South Africa [5,33,[69][70][71][72].…”

The impact of ethnicity on cochlear implantation in Norwegian children

“…Other studies have shown differences in genes coding for deafness in certain ethnic minorities [16][17][18][19][20]. Alternative explanations could be infections, prematurity, and neonatal complications [21], but this is less likely in view of the evenly distributed comorbidity in the present study.…”

The genetic basis of deafness in populations of African descent

“…The GJB6-D13S1830 deletion and the mitochondrial mutations were also not observed in this group (Kabahuma et al, 2011). GJB2 mutations were also absent among deaf probands from the Yoruba tribe residing in Ibadan, a suburban city in Nigeria (Lasisi et al, 2014). Similarly, an analysis of a large cohort of Ugandan deaf patients identified none of the common GJB2 deletions (Javidnia et al, 2014).…”

“…Studies among African populations reported that pathologic GJB6 mutations have been widely screened but not identified. Specifically, they were found to be absent in African populations within South Africa (Kabahuma et al, 2011), Nigeria (Lasisi et al, 2014), Cameroon (Bosch et al, 2014), Brazil (Batissoco et al, 2009) and the United States Samanich et al, 2007).…”