Nonsyndromic Deafness, X-Linked

What is nonsyndromic deafness, X-linked?

Nonsyndromic deafness is hearing loss that is not associated with other signs and symptoms. In contrast, syndromic deafness involves hearing loss that occurs with abnormalities in other parts of the body.

Nonsyndromic deafness is often genetic and can be described by its pattern of inheritance. An X-linked inheritance pattern means that the gene responsible for the condition is located on the X chromosome (one of the two sex chromosomes). X-linked nonsyndromic deafness is designated DFN. Each type is also numbered in the order in which it was described. For example, DFN3 was the third described form of X-linked nonsyndromic deafness.

Nonsyndromic deafness, X-linked is a subtype of nonsyndromic deafness.

X-linked nonsyndromic deafness may be present from birth or early childhood (prelingual or congenital), or may occur later in childhood or adolescence, after the development of speech (postlingual). The hearing loss may be stable or may become more severe over time.

Most forms of X-linked nonsyndromic deafness are sensorineural, which means they are caused by changes to structures in the inner ear. The inner ear consists of three parts: a snail-shaped structure called the cochlea that helps process sound, nerves that send information from the cochlea to the brain, and structures involved with balance.

Hearing loss that results from changes in the middle ear is called conductive hearing loss. The middle ear contains three tiny bones that help transfer sound from the eardrum to the inner ear.

DFN3 is the most common form of X-linked nonsyndromic deafness. It involves both sensorineural hearing loss and conductive hearing loss; this combination is called mixed hearing loss. In people with DFN3, one of the small bones in the middle ear (the stapes) cannot move normally, which interferes with hearing. This characteristic sign of DFN3 is called stapes fixation.

How common is nonsyndromic deafness, X-linked?

Between 1 percent and 2 percent of all nonsyndromic deafness is inherited in an X-linked pattern. DFN3 is the type of X-linked deafness that occurs most frequently.

What genes are related to nonsyndromic deafness, X-linked?

Mutations in the POU3F4 gene cause nonsyndromic deafness, X-linked.

Only one gene responsible for X-linked nonsyndromic deafness has been identified. This gene, POU3F4, causes the DFN3 form of deafness. Mutations in the POU3F4 gene disrupt the normal development of structures in the inner and middle ear, resulting in hearing loss.

At least four other regions of the X chromosome are involved in hearing loss, but the responsible genes have not been discovered.

How do people inherit nonsyndromic deafness, X-linked?

X-linked conditions are caused by mutations in genes on the X chromosome, one of the two sex chromosomes. In males (who have only one X chromosome per cell) one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes per cell), a mutation typically must be present in both copies of the gene to cause hearing loss. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

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.

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