Objective: Hearing loss (HL) is the most prevalent sensorineural defect in human. Mild to severly Profound HL occurs in about l.0 per 1000 births. Many previous studies have shown that about 50% of deafness is due to genetic factor and 50% is due to environmental and etiologically unknown. In this study, we are searching the causes of deafness at these families and introduce strategies for diagnosis and prevention.

Materials & Methods: Questionaires were distributed in deaf schools, hearing loss and rehabilitation centers in Qom and Markazi provinces collecting done after filling by the parents. The criterias such as age, sex, number of deaf individuals in families their close relatives, the marriage type of the parents and etiology of disease (if it is genetic or environmental) were extracted from questionnaires and were analysed by SPSS software.

Results: Three hundred and fifty four (354) Questionnaires contained complete information from hearing loss families were collected. Age mean of proband individuals is 16.1±8.1. Sex distribution of 48.4% and 51.6% girls and boys, respectively. Parents were 59.3% and 36.7% of consanguineous and unfamilial marriage, respectively. The marriage type of were not determined in 4%. Mean of deaf individuals among these families was 1.8±1.4.By assessing the filled questionnaires and pedigrees. The deafness etiology in the studies population was categorized as genetic cause (70.9 %), environment factor (9%) and unknown etiology (20.1%).

Conclusion: Genetic factor with and autosomal recessive inheritance pattern was the most common cause of hearing loss due to the high prevalence of consanguineous marriage which resulted and increased genetic causes in more than 50%. Multiplicity of offspring also shawn an increased in frequency of hearing loss in families that have deaf with genetic background of this disorder. In this study, environmental and unknown factors are second cause of HL. We may interestingly reduce frequency of HL in Iran with discouraging consanguineous marriage, health education, population regeneration control also genetic counseling especially for high risk families.