Objective: To investigate, in a prospective study, the incidence of homozygotes and heterozygotes of the 35delG/GJB2 mutation for connexin 26 in the low-risk population of newborns undergoing two-stage universal neonatal hearing screening (UNHS).
Patients and methods: The study population consisted of 1048 neonates born at the Department of Obstetrics and Gynecology, Rijeka University Hospital, Croatia, in the period between March 1, 2005 and June 30, 2005. The neonates underwent a two-stage UNHS program that included evoked otoacoustic emission (E-OAE) in all infants and automated auditory brainstem response (A-ABR) in those who did not pass the E-OAE. The 35delG/GJB2 mutation was determined in the umbilical cord blood of all examinees.
Results: Fifteen out of 1048 infants (14.3 per 1000) did not pass the E-OAE, of whom three (2.86 per 1000) did not pass the A-ABR (two unilateral, one bilateral). The 35delG/GJB2 mutation was found in 13 out of 1033 infants who did pass the E-OAE and in one who did not pass the E-OAE. Thirteen out of 14 infants were heterozygotes (12.4 per 1000) and one infant was homozygote (0.95 per 1000) for the 35delG/GJB2 mutation. The homozygous infant had a bilateral pathological result on E-OAE and A-ABR, while 13 infants who were homozygotes passed the E-OAE.
Conclusion: In all neonates, regardless of hearing impairment, genetic testing for the 35delG/GJB2 mutation is desirable in southern Croatia. The incidence of affected homozygous and healthy heterozygous transmitters of the 35delG/GJB2 mutation was in concordance with findings in southern European countries.