DNA copy number analysis of the DFNB1 hereditary hearing loss locus

Abstract

Recessive mutations in the GJB2 gene and large deletions of the cis-regulatory element of this gene are the main causes of congenital nonsyndromic sensorineural hearing loss in many countries, including Russia. Large deletions represent 0.3–10% of all alleles in the DFNB1 locus in different populations and are usually observed in compound heterozygous state with intragenic mutations or are rarely observed in the homozygous or compound-heterozygous state with another large deletion. According to published studies, six large deletions exist, including three frequent deletions del(GJB6-D13S1830), del(GJB6-D13S1854), and del(GJB2-D13S175) and three rare deletions observed in single cases. The present study describes the results of the copy number analysis of the GJB2 regulatory region for the detection of unknown deletions in patients with a single heterozygous recessive intragenic mutation. Additionally, a quantitative analysis of GJB2 and GJB6 gene sequences in individuals bearing homozygous mutation in the GJB2 gene, which might also have mutation in the hemizygous state, is performed. The system for quantitative analysis of the region including the regulatory element of the GJB2 gene based on the MLPA® approach is developed. Moreover, a commercial kit of reagents is used for the detection of copy number of the GJB2 and GJB6 genes by the same method. As a result of the conducted analysis, no changes in copy number are detected in the explored regions. Obviously, if Russian patients have mutations in unidentified regulatory or other regions of the DFNB1 locus, frequency of such unidentified mutations is extremely rare.