Background: The del35G mutation in the GJB2 gene is the most common causeof prelingual deafness. The mutation frequency has so far been estimated either by testing symptomaticchildren or adults, or by carrier testing of the general population. The purpose of our study was toestablish the incidence of the del35G/GJB2 mutation in newborns with hearing impairment - in congenitaldeafness. Material/Methods: Patients were identified through a neonatal screening program (performedon a regular basis in Croatia since 2002). Otoacoustic emission testing was performed on 3275 newborns,and allele-specific PCR was performed on newborns diagnosed with hearing impairment. Results: Hearingimpairment was found in 9 newborns, the frequency of congenital hearing impairment being 1/363; the del35Gmutation was found in 3 of these 9 newborns. The established incidence of the mutation in the studiedpopulation of Croatian newborns with hearing impairment is 1/1091 (95CI: 1/372-1/3205). Conclusions:This particular approach to patient identification, based on exact clinical examination supplementedwith molecular testing, allowed for complete diagnosis and precise estimation of the incidence of themutation in cases of congenital deafness, which proved to be higher than previously reported in prelingualdeafness. This finding has important implications in clinical evaluation and genetic counseling of patientsand their families.

Keywords: Connexins - genetics, Alleles, Croatia, Deafness - epidemiology, Gene Frequency, genetic testing, Incidence, Infant, Newborn, Mutation, Otoacoustic Emissions, Spontaneous, Sequence Deletion