Hearing loss and deafness are the most frequent sensory defects in humans. Inborn hearing losses affect every 1000th neonate and more than half are genetically based. The majority (some 80%) of genetically conditioned, non-syndromic hearing losses are autosomally recessively inherited.Mutations in the gene for connexin 26 (Cx26) cause the major part (up to 50 %) of autosomal recessive and thus also genetically conditioned heating losses. In this gene there is in the European population a highly prevalent mutation - deletion of base G in position 35 (35delG). The frequency of healthy heterozygous carriers of this mutation in the hearing European population is high, almost 3 % (1:31). In the submitted paper the authors present the first results of examinations of Cx26 gene in a group of Czech patients with congenital non-syndromic hearing loss. Eleven patients from nine families with congenital hearing loss without a proved acquired cause were examined for the presence of mutations in Cx26 gene. The examination had two stages - first focused on the presence of the most frequent mutation - 35delG - and subsequently in all patients sequencing of the whole coding section of the Cx26 gene wasmade. In eight patients from six families the most frequent mutation in 35delG in the homozygous state was proved, in three patients no deviation as compared with the published sequence of the Cx26 gene was proved, not even by direct sequencing. Their impaired hearing is thus due to a disorder of another gene or is acquired, the cause being unknown. Furthermore the authors made for the first time in the Czech Republic a prenatal examination in a family with a child with congenital hearing loss where the result in the foetus was favourable and the parents decided for continuation of the pregnancy. The results indicate, although so far only based on a small group, that also in the Czech population mutations in the Cx26 are in the majority of patients the cause of inborn hearing loss and that mutation 36delGis also in our country the most frequent mutation in the Cx26 gene in these patients. K e y w o r d s: congenital hearing loss, inborn deafness, connexin 26.

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