Usher Syndrome Type III
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Usher Syndrome Type III is distinguished from other forms of Usher syndrome by its progressive hearing loss, in contrast to the stable congenital hearing loss seen in Types I and II. Combined with retinitis pigmentosa causing progressive vision loss, Type III leads to dual sensory impairment that worsens over time. While rarer than Types I and II worldwide, Type III is the most common form in Finland and among Ashkenazi Jews.
Children with Usher Type III typically develop normal or near-normal hearing in infancy and early childhood. Hearing loss begins later, usually in the first or second decade of life, and progresses from mild to severe or profound over years to decades. This progressive nature means that individuals often develop spoken language normally before experiencing significant hearing decline.
Vision problems follow a similar progressive pattern. Night blindness and peripheral vision loss typically begin in the second decade of life and gradually worsen. The rate of progression is variable—some individuals retain functional vision into middle age, while others experience more rapid decline. Balance problems may or may not be present and are generally less severe than in Type I.
Usher Type III is primarily caused by mutations in the CLRN1 gene, which encodes a protein called clarin-1 that is important for the function of hair cells in the inner ear and photoreceptor cells in the retina. The condition is inherited in an autosomal recessive pattern. A specific founder mutation (N48K) is particularly common in Finnish and Ashkenazi Jewish populations. Hearing aids, cochlear implants, and low vision aids can help maintain function as sensory abilities decline.
NutraHacker examines the following gene related to Usher Syndrome Type III:
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