Audiologic and molecular screening for hearing loss by 35delG mutation in connexin 26 gene and congenital cytomegalovirus infection

Hearing loss may be attributed to genetic and environmental factors. Mutations in the gene of the CX26 protein (connexin 26), are responsible for 30-80% of all cases of non-syndromic profound hearing loss. The 35delG is the most frequent variant in the caucasian population. As to environmental factors, the cytomegalovirus (CMV) is the main cause of congenital infection. To determine the prevalence of congenital CMV infection and the frequency of the 35delG mutation in newborns. To identify those at risk of suffering hearing loss in order to do an audiologic follow-up of detected cases. One thousand and twenty samples of dry blood spots corresponding to newborns were tested using conventional and real time PCR. Audiologic screening was performed to all newborns before hospital discharge. Fifteen out of 1020 subjects were heterozygous for the mutation. No homozygous patients were found. Six out of the samples tested positive for CMV (confirmed by a urine sample), out of which only one newborn was symptomatic. The auditory brainstem response was recorded in all these children. Hearing loss was found in three children with congenital CMV infection and two with 35delG mutation. The frecuency of 35delG mutation carriers in our population was 1.3% and the CMV congenital infection prevalence was 0.6%. Audiologic monitoring of these two populations allowed detection of hearing loss of late onset.