Usher Syndrome: Type IB

Usher syndrome type I (USH1) is an inherited disorder that causes hearing loss at birth and progressive vision loss starting in adolescence. The vision loss begins as night blindness in early adolescence followed by a gradual loss of peripheral vision. Development of cataracts may further reduce vision. Children with USH1 also learn to sit and walk at a later age than other children and have balance problems as they grow older. The life expectancy and intellect of individuals with USH1 is not affected. Without help from a cochlear implant, individuals typically do not develop speech. USH1 is caused by pathogenic variants in several genes, including MYO1A, USH1C, CDH23, and PCDH15.

Usher syndrome type I is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

There are generally no signs or symptoms associated with being a carrier for USH1. However, the risk to have a child affected with USH1 is increased. Testing of reproductive partners is recommended for carriers of USH1.

Usher syndrome is estimated to occur in approximately 3 to 6 per 100,000 newborns in Northern Europe and at least 4 in 100,000 newborns in the general US population. Usher syndrome is divided into three major types, I, II, and III. Type I is estimated to occur in about 1 in 25,000 newborns.

Genetics Home References: Usher syndrome (http://ghr.nlm.nih.gov/)

OMIM [USHER SYNDROME, TYPE I: 276900] (http://www.ncbi.nlm.nih.gov/omim)
Gene Reviews: Usher Syndrome Type I (http://www.ncbi.nlm.nih.gov/books/NBK1116/)

• Full gene sequencing