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 aetiology 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 mutations 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 nine 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 aetiology of HL in this population.

Keywords: GJB2; GJB6 deletion; Molecular diagnosis; Nigeria; Non-syndromic deafness; mtDNA mutation.

Figure 1

Contribution of GJB2 mutations to non-syndromic deafness among the populations in SSA