![]() The types are further divided into subtypes based on their genetic cause. These types are distinguished by the severity of hearing loss, the presence or absence of balance problems, and the age at which signs and symptoms appear. Researchers have identified three major types of Usher syndrome, designated as types I, II, and III. However, many people with retinitis pigmentosa retain some central vision throughout their lives. In some cases, vision is further impaired by clouding of the lens of the eye (cataracts). Over time, these blind spots enlarge and merge to produce tunnel vision. Loss of night vision begins first, followed by blind spots that develop in the side (peripheral) vision. Vision loss occurs as the light-sensing cells of the retina gradually break down. The loss of vision is caused by an eye disease called retinitis pigmentosa (RP), which affects the layer of light-sensitive tissue at the back of the eye (the retina). The hearing loss is classified as sensorineural, which means that it is caused by abnormalities of the inner ear. Usher syndrome is a condition characterized by partial or total hearing loss and vision loss that worsens over time. The locus designation USH2B has been withdrawn see HISTORY. USH2D (611383) is caused by mutation in the WHRN gene (607928). USH2C (605472) can be caused by mutation in the ADGRV1 gene (602851) or by biallelic digenic mutation in the ADGRV1 and PDZD7 (612791) genes. Usher syndrome type II is genetically heterogeneous. Genetic Heterogeneity of Usher Syndrome Type II See 276900 for clinical characterization of Usher syndrome types I, II, and III. Type II is the most common of the 3 Usher syndromes (Eudy et al., 1998). In brief, patients with Usher syndrome type II have mild hearing impairment with normal vestibular responses. ![]() It is the most frequent cause of combined deafness and blindness in adults and affects 3 to 6% of children born with hearing impairment. Usher syndrome is a clinically and genetically heterogeneous autosomal recessive disorder characterized by sensorineural hearing deficiencies at birth and later development of progressive retinitis pigmentosa (RP).
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