Deafness is the most frequent sensorial defect in human beings and it may have different
causes since environmental to hereditary. In developed countries the estimates suggest that in
each 1000 births some kind of deafness is expressed and more than 60% of the cases have a
genetic origin. In Brazil, the hereditary deafness is not well-known. It is believed that four in
each thousand newborns express some kind of hearing defect and that the frequency of
deafness caused by genetic factors is estimated in 16%, while the 84% remaining cases are
caused by environmental factors and have an unknown etiology. The many forms of
hereditary deafness already identified are very rare, except for the one which is caused by
mutations in the GJB2 gene which codifies the connexin 26. The connexins represent a class
of a protein family which is responsible for the formation of communications channels
between adjacent cells (Gap Junctions), this communication is fundamental for the growth
and differentiation of the tissues. Until now there have been described 102 mutations of GJB2
gene which are associated to the hereditary deafness. Three mutations stand out because they
have high frequency in specific population groups: 35delG among Europeans and Brazilians,
167delT among Ashkenazi Jews, and 235delG among Asians. In this study, we performed a
molecular analysis of the entire coding sequence of the GJB2 gene (Connexin 26) in a
population sample consisted of 30 unrelated individuals with prelingual nonsyndromic
sporadic deafness from the population of Belém do Pará. DNA was obtained by peripheral
blood samples and analyzed by the conventional PCR followed by automatic sequencing.
Mutations in the Connexin 26 gene were found in 20% of the sample (6/30). The mutations
35delG and R143W were observed in one patient (1/30), both in the heterozygous and related
to the patient’s deafness. Two additional mutations were observed in different individuals:
G160S in a patient corresponding to 3.3% (1/30), and V27I was observed in 4 patients with
allele frequency of 0.08; however mutations G160S and V27I are not related deafness. In this
work the observed frequencies of mutations are equivalent to the frequencies observed in
other populations previously studied. These results indicate that mutations in the GJB2 gene
are important causes of deafness in our region and it cannot be excluded that the possibility of
deafness presented by some individuals may be caused, mainly, by environmental factors
such as infectious processes occurring during pregnancy or the first months of life.
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