Clinical and genetic characterisation of childhood-onset sensorineural hearing loss reveal associated phenotypes and enrichment of pathogenic founder mutations in the Finnish population

To examine the clinical and genetic characteristics of childhood-onset bilateral sensorineural hearing loss (SNHL) in Finland. Retrospective analysis. A total of 249 children younger than 18 years were diagnosed with bilateral SNHL in Oulu University Hospital, Finland, from 2017 to 2022. Pathogenic or likely pathogenic gene variants or chromosome abnormalities explaining SNHL were identified in 41% (<i>N</i> = 101/249) of children. Likely causative variants were more commonly identified in patients with severe SNHL than in those with moderate or mild SNHL. Our study identified likely causative gene variants in 24 different genes and six different likely causative chromosome abnormalities, demonstrating the genetic heterogeneity of SNHL. Population-enriched founder mutations were identified in the <i>CABP2</i>, <i>CLRN1</i>, <i>MYO7A</i>, <i>SUCLA2</i>, <i>TMC1</i>, and <i>TWNK</i> genes. A significant number of patients had associated phenotypes, including global developmental delay or intellectual disability (16%), language disorder (20%), ophthalmological abnormalities (16%), or malformations other than those involving the ear (10%). SNHL is genetically and clinically heterogeneous. Pathogenic variants in <i>GJB2</i> were the most common. Several population-enriched variants were identified as causing SNHL in the northern Finnish population. Associated medical phenotypes are common and should be taken into account in patients’ follow-up and treatment.