Usher syndrome
Usher syndrome is a genetic condition characterized by a combination of hearing loss and progressive vision loss caused by retinitis pigmentosa.
Overview
Usher syndrome involves sensorineural hearing loss and vision loss due to retinitis pigmentosa (RP), a disease that causes the light-sensitive cells of the retina to break down. Vision loss typically begins with night blindness, followed by the development of blind spots that eventually lead to tunnel vision.
Types of Usher Syndrome
- Type I: Characterized by severe to profound hearing loss from birth, childhood-onset vision loss, and vestibular (balance) abnormalities.
- Type II: Involves hearing loss from birth (ranging from mild to severe) and progressive vision loss beginning in adolescence or adulthood. It is not associated with balance problems.
- Type III: Features normal hearing at birth, with hearing and vision loss developing in late childhood or adolescence. Balance problems may occur in some individuals.
Causes
Usher syndrome is caused by mutations in several different genes, including MYO7A, CDH23, USH2A, and CLRN1. These genes provide instructions for proteins essential to the development and function of hair cells in the inner ear (for hearing and balance) and photoreceptor cells in the retina (for vision). Mutations lead to the degeneration of these sensory cells.
Inheritance
All types of Usher syndrome are inherited in an autosomal recessive pattern. This means that both copies of the gene in each cell must have a mutation for the condition to occur. Parents of an affected individual are carriers, each possessing one mutated copy of the gene, but they do not show signs or symptoms of the syndrome.