Introduction: Hereditary hearing impairment is a heterogeneous disorder showing different pattern of inheritance and involving a multitude of different genes. Mutations in the GJB2 gene, especially the 35delG mutation, have been established as a major cause of inherited and sporadic non-syndromic deafness in different populations. Mutations in GJB2 gene, encoding gap junction protein (Connexin 26), may be responsible for up to 50% of cases of autosomal recessive non-syndromic hearing impairment and in 15-30% of sporadic cases.
Study design: The authors analyzed 15 north east Hungarian families and 30 sporadic cases with nonsyndromic hearing impairment for the 35delG mutation.
Methods: DNA were tested for the common 35delG mutation by a polymerase chain reaction based restriction enzyme assay (BsiYl).
Results: Fifty two patients showing a homozygous 35delG mutation were audiological examined. Ordinarily these patients showed a prelingual, sensorineural, bilateral, symmetric hearing loss without progression. The audiograms were characterized by sloping or flat patterns. The carrier frequency of the 35delG mutation among control group was 5.1%.
Conclusion: The phenotypic manifestation varied in 30% of all analyzed patients, making genetic counseling extremely difficult. Due to this knowledge mutation analysis of GJB2 cannot distinctly predict the degree of hearing impairment.