EVALUATION OF EPIDEMIOLOGIC FACTORS IN PATIENTS WITH CONGENITAL HEARING IMPAIRMENT

Hearing impairment is the predominant hereditary sensorineural defect in humans. It is a heterogeneous trait and an estimated 50% of congeni tal hearing impairment is caused by genetic defects. About 70% of the cases of congenital deafness are non-syndromic, following the autosoma l recessive mode of inheritance. Examination of cases of profound cong enital bilateral sensorineural hearing loss in an attempt to classify the association with epidemiological parameters and birth order of pro positii revealed a higher preponderance of males as compared to female s of both familial and sporadic cases. The rate of parental consanguin ity was also high (37%) as compared to the incidence reported in the l ocal population, indicating the presence of rare recessive genes. Pedi gree analysis revealed that the majority of cases (79%) followed a rec essive mode of inheritance. In both familial and sporadic cases a grea ter proportion of patients (86.6%) were of early para 46% of them were primiparous, indicating greater risk of hearing impairment in childre n born early. When tested for association with birth rank, only the fe male probands of sporadic cases showed a significant association with later para, indicating the involvement of a fresh dominant mutation. ( C) 1998 Chapman & Hall Ltd.