engleski

Evaluation of Hereditary Hearing Impairment in Croatia coupling newborn screening program with genetic testing for common mutations

Hearing impairment with the prevalece of about 1 in 1000 children is the most prevalent sensory deficit in humans. It is generally thought that more than half the cases of childhood deafness are genetically determined, while the rest are due to environmental causes. In the past decade significant progress has been made in the identification of deafness genes and in the knowledge of the molecular processes involving the proteins they encode. Based on the prevalence date, we can expect that about 50 newborns with severe hearing impairment will be born in Croatia every year. Until recently little has been done for early detection and etiological evaluation in these children. In 2002 we introduced a national programme of universal newborn screening for early diagnosis of hearing impairment in all Croatian neonatal wards. This will allow early intervention, which will hopefully greatly improve the adaptation, communication skills and final outcome in affected children. Implementation of the screening programme and identification of hearing loss in newborns prompted us to consider the development of a rational clinical approach to the evaluation of individuals with hearing impairment including the introduction of molecular diagnostic tests for the most common mutations associated with deafness. A single gene, GJB2, which encodes the connexin 26 molecule, has been found to cause the majority of autosomal recessive nonsyndromic deafness in Mediterranean populations. The gene is small and relatively easy to screen. Moreover, it is estimated that two mutations - 35delG and 167delT which prevail in the populations of Europe diagnose up to 50% of autosomal recessive deafness and 10-40% of sporadic cases. In any patient in whom a definitive diagnosis cannot be established on the basis of family history, physical evaluation and laboratory testing, molecular testing for Cx26 mutations will be performed (nonsyndromic sporadic cases, and cases compatible with recessive type of inheritance). In prospect we would like to develop other tests for the most common mutations associated with deafness. In this way we would be able to provide timely and more accurate genetic counselling for affected families.

hereditary hearing impairment; screening; genetic testing

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