Usher syndrome type 3 is is the rarest form of Usher syndrome, characterized by later onset hearing loss, RP that manifests between the second and fourth decades of life and variable vestibular dysfunction. Forty-two percent of those with Usher syndrome in Finland are thought to have USH3. It is also found in individuals of Ashkenazi Jewish heritage.
Hearing in Type 3
Individuals are born with normal hearing. Hearing loss begins during late childhood or adolescence and progresses to profound hearing loss.
Vision in Type 3
Children born with Usher type 3 have retinitis pigmentosa (RP) that manifests in later childhood or early adolescence.
Vestibular Function in Type 3
Vestibular (balance) function is typical at birth and may become affected in some with Usher 3 in adult years.
Genes involved in Type III
To date, only mutations in the CLRN1 (USH3A) and HARS (USH3B) genes are known to cause this type of Usher syndrome. Identified disease causing mutations in these genes include missense, nonsense, frameshift, splice-site as well as deletions distributed across nearly all exons.
