Genetic Basis of Nonsyndromic Sensorineural Hearing Loss in the Sub-Saharan African Island Population of São Tomé and Príncipe: The Role of the DFNB1 Locus?

Hearing loss (HL) is a common condition with both genetic and environmental causes, and it greatly impacts global health. The prevalence of HL is reportedly higher in developing countries such as the Sub-Saharan African island of São Tomé and Príncipe, where the deaf community is estimated to be less than 1% of the population. We investigated the role of the DFNB1 locus (GJB2 and GJB6 genes) in the etiology of nonsyndromic sensorineural hearing loss (NSSHL) in São Tomé and Príncipe. A sample of 316 individuals, comprising 136 NSSHL patients (92 bilateral, 44 unilateral) and 180 controls, underwent a clinical and audiological examination. Sequencing of the GJB2 coding region and testing for the (GJB6-D13S1830) and del(GJB6-D13S1854) GJB6 deletions were performed. A total of 311 out of 316 individuals were successfully analyzed regarding the GJB2 and GJB6 genetic variations, respectively. The frequency of the GJB2 coding mutations in patients and controls was low. Some of those coding mutations are the most commonly found in Eurasian and Mediterranean populations and have also been identified in Portugal. None of the GJB6 deletions was present. The presence of certain coding variants in São Tomé and Príncipe suggests a non-Sub-Saharan genetic influx and supports the previously reported genetic influx from European (mainly Portuguese) ancestors. In summary, DFNB1 locus does not appear to be a major contributor to NSSHL in São Tomé and Príncipe. However, the presence of both pathogenic and likely pathogenic mutations in GJB2 suggests that GJB2-related NSSHL might still occur in this population, warranting further research on GJB2 testing in NSSHL cases.