GENETIC TESTINGVolume 5, Number 2, 2001Mary Ann Liebert, Inc.

High Frequency of GJB2 Gene Mutations in Polish Patientswith Prelingual Nonsyndromic Deafness

WOJCIECH WISZNIEWSKI,1 LUCJA SOBIESZCZANSKA-RADOSZEWSKA, 2

EWA NOWAKOWSKA-SZYRWINSKA, 2 EWA OBERSZTYN,1 and JERZY BAL1

ABSTRACT

We report an analysis of 102 unrelated Polish patients with profound prelingual deafness for mutations inthe GJB2 gene (OMIM #220290). Mutations were found in 41/102 (40%) subjects. Among mutated alleles,35delG was prevalent and present in 88%. In nine alleles, different mutations were found: M34T, Q47X,R184P, and 313del14 (found in 6 patients). The results prove mutations in the GJB2 gene are responsible formuch hereditary nonsyndromic deafness in Poland, with a strong prevalence of the 35delG mutation. We havealso found a high carrier frequency (1/50) for the 35delG mutation in the Polish population.

147

INTRODUCTION

PARTIAL OR COMPLETE SENSORINEURAL HEARING LOSS is oftenof congenital origin. According to epidemiological data the

incidence of childhood deafness is estimated at 1–2/1000.Hereditary deafness may be progressive, and the degree of hear-ing impairment is usually severe. The etiology of hearing lossin children leads to confusion in clinical diagnosis and geneticcounseling. Those difficulties come from the clinical picture ofdeafness that usually (in 70% of cases) appears as a single symp-tom (isolated, nonsyndromic deafness). In the remaining 30%cases, it is accompanied by other symptoms or dysmorphic fea-tures (Petit, 1996). It is estimated that 100 different genes areinvolved in the nonsyndromic form of deafness. Among iso-lated cases of deafness, the autosomal recessive forms (DFNB)are markedly prevalent (80%). Among those genes, one in par-ticular, GJB2 mapped to locus DFNB1 on chromosome 13(13q11), seems to be responsible for a high proportion of cases.The gene is composed of 2300 bp and encodes connexin 26, agap junction protein. Mutations in the GJB2 gene were observedin 50% of families affected with profound prelingual, autoso-mal recessive deafness in many European countries (Kelsell etal., 1997). The aim of this work was to estimate the frequencyof mutations in the GJB2 gene in a cohort of Polish patients af-fected with autosomal recessive, nonsyndromic deafness.

MATERIALS AND METHODS

One hundred and two children affected by profound prelin-gual deafness were studied. Most of them were referred to theDepartment of Audiology of the Institute of Mother and Child(Warsaw) from the High School for Deaf Children in Warsaw.Informed consent was obtained from all subjects and from par-ents of under-aged patients. For all patients, a detailed history,including prenatal and perinatal periods, was taken to excludeenvironmental causes of deafness. It was followed by preciseclinical examination including general, audiological, and psy-chological evaluations to exclude syndromic forms of deafness.To determine the carrier frequency of the 35delG mutation ina Polish population, 150 samples were analyzed. The sampleswere unrelated, random controls with a normal male/female sexratio. Blood samples were obtained from subjects, and genomicDNA was extracted according to standard protocols. Screeningfor the 35delG mutation was performed by allele-specific oligonucleotide (ASO) hybridization, using oligonucleotideprobes and hybridization conditions as previously described(Rabionet and Estivill, 1999). For the non-35delG mutationanalysis, the entire coding sequence (exon 2) of the GJB2 genewas amplified, using standard primers and conditions (De-noyelle et al., 1997). The fragments of 770 bp were subse-quently sequenced on an ABI 310 sequencer (Perkin Elmer).

1Department of Medical Genetics, Institute of Mother and Child, Warsaw, Poland.2Department of Audiology, Institute of Mother and Child, Warsaw, Poland.

RESULTS AND DISCUSSION

Molecular analysis of the GJB2 gene was performed in agroup of 102 deaf children. All subjects presented with bilat-eral, sensorineural, and nonsyndromic deafness. In all cases, en-vironmental causes and syndromic associations were excluded.Mutations in the GJB2 gene were found in 41/102 (40%) ofsubjects. Among the mutated alleles, the most prevalent,35delG, accounted for 88% of cases. In nine alleles differentmutations were detected: M34T, Q47X, and R184P (one each),and 313del14 (found in 6 patients). In the 61 remaining pa-tients, no mutation in GJB2 exon 2 was detected. In the pres-ent study, the analysis of noncoding exon 1 sequence was ex-cluded, but it seems unlikely that patients would carry twomutations in that region. It may be presumed that mutations inloci other than DFNB1 may cause the phenotype.

We have also analyzed the carrier frequency of 35delG in150 unrelated, random subjects. The mutation was detected inthree cases, which gives a carrier frequency of 1/50. The re-sults are very similar to data obtained for other central Euro-pean populations (Gasparini et al., 2000).

The results probe that mutations in the GJB2 gene are re-sponsible for a large proportion of hereditary nonsyndromicdeafness in Poland, with a strong prevalence of the 35delG mu-tation. The calculated frequency of GJB2 mutations found in

an analyzed cohort of patients (40%) is similar to the valuesobtained for other European populations: French (55%) andSpanish (40%) (Gasparini et al., 2000).

ACKNOWLEDGMENTS

This study was partially supported by Komitet BadanNaukowych grant number 4 PO5E 081 16. W.W. was supportedby the School of Molecular Medicine and the Foundation ofPolish Science.

REFERENCES

DENOYELLE, F., WEIL, D., MAW, M., WILCOX, S., LENCH, N.,and OSBORN, A. (1997). Prelingual deafness: high prevalence of a30delG mutation in the connexin 26 gene. Hum. Mol. Genet. 6,2173–2177.

GASPARINI, P., RABIONET, R., BARBUJANI, G., MELCHIONDA,S., and PETERSEN, M. (2000). High carrier frequency of the 35delGdeafness mutation in European populations. Eur. J. Hum. Gen. 8,19–23.

KELSELL, D.P., DUNLOP, J., and STEVENS, H.P. (1997). Connexin-26 mutations in hereditary non-syndromic sensorineural deafness.Nature 387, 80–83.

PETIT, C. (1996). Genes responsible for human hereditary deafness:symphony of thousand. Nature Genet. 14, 385–391.

RABIONET, R., and ESTIVILL, X. (1999). Allele specific oligonu-cleotide analysis (ASO) for the common mutation 35delG in the con-nexin26 (GJB2) gene. J. Med. Genet. 36, 260–261.

Address reprint requests to:Dr. Wojciech Wiszniewski

Department of Medical GeneticsInstitute of Mother and Child

Kasprzaka 17a01-211 Warsaw, Poland

E-mail: wojtekw@imid.med.pl

Received for publication March 28, 2001; accepted May 1,2001.

WISZNIEWSKI ET AL.148

TABLE 1. THE RESULTS OF GJB2 GENE ANALYSIS

Genotype Results

Allele 1 Allele 2 Number %

35delG 35delG 32 3135delG 313del14 6 635delG M34T 1 135delG Q47X 1 135delG R184P 1 1WT WT 61 60

Total 102 100