There are two main factors leading to deafness: heredity and external environment. According to the etiological study of hearing impairment, about 60% of deaf patients in the world are related to heredity. Moreover, the population of deaf gene carriers in China is very large, and the deaf gene carrier rate of normal people is about 4% to 6%. The Molecular Diagnosis Center for Deafness of Beijing 30 1 Hospital conducted 10880 deafness gene tests in 28 provinces and cities in China, and found that 6 out of every 100 normal hearing population carried deafness mutation genes.

Many hereditary deafness is inherited by autosomal recessive inheritance. If the parents carry the same deafness gene, the child has a 25% probability of being a child in congenital deafness and a 50% probability of being a deaf gene carrier. This also explains why parents with normal hearing will give birth to deaf children. Clinical data show that 90% of deaf children's parents have normal hearing.