Nonsyndromic deafness

Nonsyndromic deafness can occur at any age. Hearing loss that is present before a child learns to speak is classified as prelingual or congenital. Hearing loss that occurs after the development of speech is classified as postlingual.

Nonsyndromic deafness can have different patterns of inheritance. Between 75% and 80% of cases are inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Usually, each parent of an individual with autosomal recessive deafness is a carrier of one copy of the altered gene. These carriers do not have hearing loss.

Another 20% to 25% of nonsyndromic deafness cases are autosomal dominant, which means one copy of the altered gene in each cell is sufficient to result in hearing loss. People with autosomal dominant deafness most often inherit an altered copy of the gene from a parent who has hearing loss.

Between 1% and 2% of cases show an X-linked pattern of inheritance, which means the mutated gene responsible for the condition is located on the X chromosome. Males with X-linked nonsyndromic deafness tend to develop more severe hearing loss earlier in life than females who inherit a copy of the same gene mutation. Fathers will not pass X-linked traits to their sons since they do not pass on the X chromosome to their male offspring.

Mitochondrial nonsyndromic deafness, which results from changes to the DNA in mitochondria, occurs in fewer than 1% of cases in the United States. The altered mitochondrial DNA is passed from a mother to her sons and daughters. This type of deafness is not inherited from fathers.

Late onset progressive deafness is the most common neurological disability of the elderly. Although hearing loss of greater than 25 decibels is present in only 1% of young adults between the ages of 18 and 24 years of age, this increases to 10% in persons between 55 and 64 years of age and approximately 50% in octogenarians.

The relative contribution of heredity to age-related hearing impairment is not known, however the majority of inherited late-onset deafness is autosomal dominant and non-syndromic (Van Camp et al., 1997). Over forty genes associated with autosomal dominant non-syndromic hearing loss have been localized and of these fifteen have been cloned.

Treatment is supportive and consists of management of manifestations. Use of hearing aids and/or cochlear implant, suitable educational programs can be offered. Periodic surveillance is also important.[3]

About 1 in 1,000 children in the United States is born with profound deafness. By age 9, about 3 in 1,000 children have hearing loss that affects the activities of daily living. More than half of these cases are caused by genetic factors. Most cases of genetic deafness (70% to 80%) are nonsyndromic; the remaining cases are caused by specific genetic syndromes. In adults, the chance of developing hearing loss increases with age; hearing loss affects half of all people older than 80 years.