Half of hearing loss cases are due to genetic causes.
Deleterious changes in genes are the cause of many different kinds of human disorders. These genes are inherited from the mother and father and result from a chance mutation. Though genetic disorders can usually be diagnosed from symptoms, genetic testing is important for exploring the root cause of certain disorders.
Genetic Causes
According to the National Institute of Deafness and Other Communicative Disorders, half of the 4,000 infants born deaf every year have a genetic disorder; the remaining cases are either non-genetic or unknown. Of the genetic cases, 70 percent are due to recessive traits (meaning that two recessive copies need to be inherited), 15 percent are due to dominant traits (requiring only one dominant copy) and the remaining 15 percent include other forms of inheritance. Ninety percent of infants with hearing loss are born to parents who can hear.
Non-Syndromic and Syndromic
Genetic hearing loss can be divided into two main categories. Non-syndromic hearing loss, which constitutes two thirds of all genetic causes, is not associated with other signs and symptoms. Syndromic hearing loss makes up the other third, and it is accompanied by abnormalities in other parts of the body.
Genes
According to the Centers for Disease Control and Prevention, the gene GJB2 is the largest cause of genetic hearing loss. It encodes for a protein called Connexin 26, which helps change sound in the air to nerve signals in the brain within the cochlea of the ear. There are more than 400 known genetic causes of hearing loss, but GJB2 alone is estimated to be responsible for about half of all recessive cases and one third of total cases of hearing loss.
Genetic Testing
GJB2 is non-syndromic in nature. The remaining non-syndromic cases are caused by 13 dominant genes and eight recessive genes. Genetic testing involves sequencing these regions to discover the particular changes that led to the hearing loss. Knowing which genes contribute to a function is critical because researchers must know how any deviation in genetic code can interfere with the operation of a protein.
Mitochondrial DNA
Most DNA is found in the nucleus of the cell, but a number of syndromic disorders are mitochondrial conditions. These conditions originate and involve testing DNA found in the mitochondria where energy is produced rather than the nucleus. Mitochondrial DNA is inherited solely from the mother and not in any way from the father.
Tags: hearing loss, from mother, genetic causes
