© Borgis - New Medicine 3/1999, s. 44-45
Ewa Nowakowska-Szyrwińska1, Łucja Sobieszczańska-Radoszewska1, Teresa Bralczyk1, Wojciech Wiszniewski2, Ewa Obersztyn2, Tadeusz Mazurczak2 Jerzy Bal2
Identification of mutation gene gjb2 in patients with hearing impairment
1 Department of Audiology, National Research Institute of the Mother and Child, Warsaw
Head: Ewa Nowakowska-Szyrwińska, M.D.
2 Department of Medical Genetics, National Research Institute of the Mother and Child, Warsaw
Head: Prof. Tadeusz Mazurczak, M.D.
Prelingual non-syndromic deafness is the most frequent hereditary sensory defect. In more than 80% of cases, the mode of transmission is autosomal recessive. The molecular investigation was carried out in 48 patients from the audiology department in the National Research Insitute of the Mother and Child. We found mutations of the GJB2 gene in 50% of patients. GJB2 gene accounts for a large percentage of the cases of sensorineural prelingual deafness.
The frequency of inborn and early acquired hearing defects is estimated at 1-2/1000 newborn. It has been assumed that nearly 50% of cases of prelingual deafness are of genetic origin. 80% of them are transmitted in the autosomal recessive mode(1, 2, 3). One of the recently identified genes responsible for autosomal recessive deafness is GJB2, localised on the long arm of chromosome 13 in locus DFNB1. The gene encodes connexin 26 gap junction protein. Mutations found in the gene are responsible for the majority of cases with an autosomal recessive form of deafness (4, 5)
Molecular analysis of patients with deafness has not yet been done in Poland. The aim of this combined work performed by the Departments of Audiology and Genetics was to check the character and frquency of mutations of the GJB2 gene in patients with prelingual deafness.The clinical criteria applied for selection of patients were:
- bilateral profound hearing loss
- deafness as an isolated symptom
The analysis was performed in a group of 48 patients in the Audiological Clinic. The average age of patients was 14.5 and varied from 3 to 19 year. The group consisted of 22 females and 26 males. In every case an informal consent was obtained. A detailed history was taken from all patients and different examinations were performed:
- otolarygeal examinations to search for abnormalities of the nose, pharynx and ears,
- audiological examinations to estimate the form, degree and localisation of hearing deterioration,
- psychological examination to assess intelectual development.
The analysis revealed:
- prelingual and profound bilateral hearing loss (higher than 90 dB) present in 72% - tab. 1,
- familial cases of deafness present in 31.25% of subject, plus sporadic cases in 60.4%,
- otolaryngeal examinations were not informative,
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1. Whitek R. et al.: Screening all newborns for hearing loss using trancient evoked otoacoustic emission. Inter. J. of Ped. Otorhinolaryngology.1994, 29:203-217. 2. Vartainen E. et al.: Prevalence and etiology of bilateral sensorineural hearing imoairment in a Finnish childhood population, Int. J. of Ped. Otorhonolaryng. 1997, 41:175-185. 3. Pruszewicz A.: Zarys Audiologii Klinicznej Poznań 1994, Wyd. AM. 4. Kelsell D.P.: Connexin-26 mutations in hereditary non-syndromic sensorineural deafness. Nature 1997, 387; 80. 5. Zelante L.: Connexin-26 associated with the common form of non-syndromic neurosensory autosomal recessive deafness (DFNB1) in Mediterraneans. Hum. Mol. Genet. 1997, 9:160. 6.Estivill X. Connexin-26 mutations in sporadic and inherited sensorineural deafness Lancet 1998, 35-394.