In Bashkortostan, we studied patients with hereditary or sporadic hearing loss and their relatives. The total amount of samples included 132 individuals from 58 fami­lies. Hearing was assessed by puretone threshold audio­metry, acoustic impedance measuring and by detection of otoacoustic emission. The genetic character of deafness was inferred from the genealogical data. In addition, the patient’s history was analyzed in order to exclude the prenatal and postnatal effects of environmental factors. Infections, injuries of the hearing system and administra­tion of ototoxic antibiotics were taken into account. We also analyzed 55 unrelated families without any disorders.

Genomic DNA was isolated from 10 mL of peripheral blood by the standard protocol [16]. The coding exons of the GJB2 and GJB3 genes were divided into four frag­ments, obtained by polymerase chain reaction (PCR) with already published primers [17]. The genetic markers used in this study were microsatellite repeat polymorphisms (CA repeats) and they were amplified using the primers already described [17-19]. The products were resolved by polyacrylamide gel electrophoresis (PAGE) in 9% gel, stained with ethidium bromide, and visualized in UV light.

We performed both single-strand conformation poly­morphism (SSCP) and nucleotide sequence analyses; a combination of them revealed other, different mutations in the GJB2 and GJB3 genes. All 132 samples were screened to detect mutations by SSCP analysis. Some of the confor­mation polymorphisms were sequenced. The distances between the GJB2 gene and polymorphic markers are given in Fig. 1.

Linkage disequilibrium values were estimated by using Yule’s co-efficient, i.e., DSt = (p₁₁–p₁₂)/ Op(p₁₁+p₁₂–2p₁₁p₁₂) where p₁₁ is the frequency of allele A₁ on chromosomes carrying allele B₁, and p₁₂ is the fre­quency of allele A₁ on chromosomes carrying allele B₂ [18].

The three locus haplotypes, D13S143, D13S292, D13S175, were determined by the maximum-likelihood method, via the EM algorithm, as implemented in the HAPLO package [19], and cross-checked by an appropri­ate computer program. Haplotype diversity and linkage disequilibrium were estimated by standard methods.

                                     D13S292                                                                           SAP18
           39       0      34   85    110                                100Kb                                            1035