Deafness is one of the most common genetic diseases in clinical practice. It is estimated that about 700 million people worldwide have a hearing loss of at least 55 dB. According to the website of the China Disabled Persons’ Federation, 21 million of the 60 million disabled people in China have a hearing disability. Hearing loss of 25 dB or more accounts for about 1% of young people, 10% of people at age 60, and rises to 50% at age 75. The prevalence of congenital deafness in newborns with severe or above is about 1/1,000, at least half of which is due to genetic factors. Jiang Hongyan, Department of Otolaryngology – Head and Neck Surgery, Hainan Provincial People’s Hospital
Hereditary hearing impairment (HHI) refers to the abnormal development or metabolic disorder of the ear caused by the deafness-causing gene from the parental generation or the newly occurred mutated deafness-causing gene, resulting in poor hearing function. The deafness gene can cause lesions in the outer and middle ear, resulting in conductive deafness; it can also affect the development of the inner ear, resulting in sensorineural deafness; and in rare cases, it can involve both the outer ear and/or middle and inner ear, resulting in mixed deafness. Sensorineural deafness occupies an important position among hereditary deafness. According to statistics, the prevalence of hereditary sensorineural deafness in children is about 1:2000 to 1:6000 in Europe and the United States.
Genetic deafness is classified into non-syndromic hearing impairment (NSHI) and syndromic hearing impairment (SHI). The clinical manifestations of NSHI are mainly simple sensorineural deafness with no abnormalities other than hearing impairment; the remaining 30% of SHI have a variety of clinical manifestations and are often associated with lesions of other organs of the body or have multiple symptoms and signs in addition to hearing impairment.
Among all types of hereditary deafness, autosomal recessive inheritance of non-syndromic deafness is the most common. A simple understanding of recessive inheritance is that a child can have a certain percentage of pure or compound heterozygous mutations in a deafness-causing gene (which does not manifest as deafness) due to the presence of a heterozygous mutation in both parents, resulting in deafness, i.e., the child can be genetically deaf even if the parents have normal hearing, and depending on the genotype it can be Pre-speech deafness (before learning to speak) and post-speech deafness (when the child is born without deafness and then gradually develops deafness, after learning to speak).
Diagnostic process of hereditary deafness. Steps in the clinical diagnosis of hereditary deafness: 1). Clinically exclude other causes of deafness, such as infections, tumors, ototoxic drugs, autoimmunity, trauma, noise damage, etc.; 2). Perform a comprehensive physical examination, laboratory and imaging examinations to detect any malformations of the inner ear or other organs of the body; 3). Detailed questioning and investigation of family history, genealogy, and analysis of the type of inheritance (dominant, recessive, sex-linked or mitochondrial maternal); 4). Further chromosomal histotyping; 5). Specific or non-specific genetic testing, also known as DNA diagnosis.
Genetic diagnosis of deafness can clarify the cause of most unexplained deafness and provide clinical assistance in the diagnosis and treatment of deafness patients. It also guides the prevention and treatment of families with hereditary deafness. For couples who are diagnosed as carriers of deafness-causing genes and have the desire to have children, genetic counseling and effective prenatal diagnosis can be used to clarify the fetal genotype and avoid the birth of deaf children, thus reducing the economic and mental burden for families of deafness patients.
Application of deafness genetic diagnosis
l Patients with unexplained deafness
Normal couples who have had deaf children
Patients with drug-related deafness
Patients with suspected family history of deafness and their offspring
unmarried or married men and women who are both deaf or one of whom is deaf
Prenatal diagnosis for couples who are carriers of deafness-causing genes
l Pre-marital screening
The First Hospital of Sun Yat-sen University, Department of Otolaryngology, has been conducting deafness genetic testing on a large scale. The scope of the test covers common deafness-causing genetic loci, and genetic tests have been performed on over 700 patients to clarify the cause of deafness. For couples who have a request to have another child, we provide related counseling and can come to the hospital at 19-22 weeks of pregnancy for prenatal diagnosis of deafness to clarify the fetal genotype. For patients who are eligible for the test, we will provide you with a free genetic test for deafness. May you be free from deafness and disease.