Incidence of the del35G/GJB2 mutation in Croatian newborns with hearing impairment.

BACKGROUND

The de135G mutation in the GJB2 gene is the most common cause of prelingual deafness. The mutation frequency has so far been estimated either by testing symptomatic children or adults, or by carrier testing of the general population. The purpose of our study was to establish the incidence of the del35G/GJB2 mutation in newborns with hearing impairment--in congenital deafness.

MATERIAL/METHODS: Patients were identified through a neonatal screening program (performed on 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

Hearing impairment was found in 9 newborns, the frequency of congenital hearing impairment being 1/363; the del35G mutation was found in 3 of these 9 newborns. The established incidence of the mutation in the studied population 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 supplemented with molecular testing, allowed for complete diagnosis and precise estimation of the incidence of the mutation in cases of congenital deafness, which proved to be higher than previously reported in prelingual deafness. This finding has important implications in clinical evaluation and genetic counseling of patients and their families.