Exome sequencing identifies known and candidate genes in hearing impairment in Cameroon

Hearing impairment (HI) is one of the most common sensory disorders globally. There is limited data on the genetics of HI in Africa. We aim to identify the genetic causes of HI in Cameroon.

We used whole-exome sequencing (WES) to study the cause of HI in multiplex families from Cameroon. Cell-based experiments using HEK293T assessed the pathogenicity of targeted variants, and a knockout mouse model was used to investigate a candidate gene.

Here, we report forty-six multiplex families totaling 106 affected individuals with HI. Most families present with non-syndromic HI (NSHI) (87%, n = 40/46). Causative variants in known genes are identified in 76% (n = 35/46) of families, including nine genes that cause both syndromic HI (SHI) and NSHI, ten that underlie NSHI, and six that cause SHI. MYO15A and TMC1 are the most common genes underlying HI and are observed in six and three families, respectively. Three candidate genes (SUN2, TGM6, and TMC3) are identified. In vitro studies find that a biallelic variant in SUN2 [c.475 G > A:p.(Val159Ile); NM_015374.3] leads to mislocalization and decreased expression in HEK293T cells. In mice, SUN2 protein expression localizes explicitly to the supporting cells of the inner hair cells. Auditory thresholds of the Sun2 knockout mice are comparable to those of wild-type, suggesting that SUN2 is not a credible HI gene.

This study reports a high diagnostic rate using WES for HI and highlights the opportunity for variant and gene discoveries in African populations. These findings inform the prospects for gene therapy in HI.