Despite these difficulties, some patterns are beginning to emerge: (i) early onset and quick progression of the hearing loss (from moderate/severe to profound) seem to be common features; (ii) middle frequencies are more severely affected, the ‘cookie-bite’ audiogram being relatively frequent; (iii) HARS2 pathogenic variants result in Perrault syndrome without neurological signs; (iv) the highest interfamilial and intrafamilial phenotypic heterogeneity is observed in KARS1, with a vast majority of diverse syndromic conditions. This evidence concerns the gene HARS2 and Perrault syndrome.