Prevalence of DFNB1 mutations in Slovak patients with non-syndromic hearing loss.

OBJECTIVES

Non-syndromic hearing loss is one of the most common genetically determined diseases in human. The incidence is approximately 1:700 and most of the cases are caused by mutations in specific locus - DFNB1, which contains two genes -GJB2 and GJB6. For the GJB2 gene following mutations are most prevalent in specific populations - 35delG, 235delC, W24X and 167delT for Caucasians, Asians, Indians and Ashkenazi Jews, respectively. Large deletions are common in GJB6 gene. Many other mutations and polymorphisms were found in DFNB1 focused non-syndromic hearing loss studies thus the establishment of optimal screening protocol should be based on population specific mutation screening studies and is an objective in our study.

PATIENTS AND METHODS

In our study samples from 273 non-syndromic hearing loss patients were screened for mutations in coding and non-coding part of GJB2 gene and large deletion in GJB6 gene - del(GJB6-D13S1830).

RESULTS

Causal mutation on both chromosomes was detected in 24.57% of patients, another 9.9% carried causal mutation on one chromosome. Totally 7 polymorphisms: V27I, M34T, F83L, 354 C→T, R127H, V153I, 684 C→A and 11 causal mutations: IVS1+1 G→A, 35delG, W24X, V37I, E47X, 167delT, V84M, L90P, 310del14, 333-334delAA, R184Q were detected. No patient carried the GJB6 deletion mutation (del(GJB6-D13S1830)).

CONCLUSION

According to our results sequencing of GJB2 coding regions and IVS1+1G→A specific detection should explain approximately 25% of sporadic NSHL cases and these two tests are relevant for use as routine screening protocol for NSHL in Slovakia. The GJB6 del(GJB6-D13S1830) mutation was not detected in any of NSHL samples therefore it is not necessary to implement it in our routine screening protocol.