*5.7.1 Glutamate receptor metabotropic 7 (GRM7)*

*GRM7* encodes a G-protein coupled receptor which plays an important role in the regulation of presynaptic neurotransmission in the mammalian brain. It is widely expressed in inner hair cells, outer hair cells, spiral ganglion, and vestibular hair cells. The expression of this gene increases with age [168]. GWAS on 3434

well-characterized individuals from different locations in Europe identified SNPs in *GRM7* causing ARHL [168]. Two more studies on an American and Saami population cohort also corroborated the potential role of *GRM7* in ARHL [169, 170].

## *5.7.2 Grainyhead drosophila homolog of 2 (GRHL2)*

GRHL2 is known to have an essential role in the development and morphogenesis of epithelia of several organs in flies, mice, frogs, and zebrafish [171]. Variants in *GRHL2* have been known to cause non-syndromic autosomal dominant hearing loss [172, 173]. Additionally, a study comprised of 2418 cases from seven different European countries emphasized the association of SNPs enriched in intron 1 of *GRHL2* with ARHL [174].
