Genetic heterogeneity in hereditary hearing loss: Potential role of kinociliary protein TOGARAM2

Hearing loss (HL) is a heterogenous trait with pathogenic variants in more than 200 genes that have been discovered in studies involving small and large HL families. Over one-third of families with hereditary HL remain etiologically undiagnosed after screening for mutations in the recognized genes. Genetic heterogeneity complicates the analysis in multiplex families where variants in more than one gene can be causal in different individuals even in the same sibship. We employed exome or genome sequencing in at least two affected individuals with congenital or prelingual-onset, severe to profound, non-syndromic, bilateral sensorineural HL from four multiplex families. Bioinformatic analysis was performed to identify variants in known and candidate deafness genes. Our results show that in these four families, variants in a single HL gene do not explain HL in all affected family members, and variants in another known or candidate HL gene were detected to clarify HL in the entire family. We also present a variant in TOGARAM2 as a potential cause underlying autosomal recessive non-syndromic HL by showing its presence in a family with HL, its expression in the cochlea and the localization of the protein to cochlear hair cells. Conclusively, analyzing all affected family members separately can serve as a good source for the identification of variants in known and novel candidate genes for HL.