Usher Syndrome: Type IIA

Usher syndrome type II (USH2) is an inherited disorder that causes moderate to severe bilateral sensorineural hearing loss at birth and progressive visual impairment beginning in the first to second decade. The hearing loss is relatively mild at low frequencies and severe at higher frequencies. Vision loss starts with night blindness and loss of peripheral vision. Eventually central vision too can be decreased. The degree of hearing and vision loss can vary even among family members. Intelligence and life-expectancy are not affected by USH2. There is no cure for Usher syndrome type II; however, hearing aids are helpful. USH2 is caused by pathogenic variants in three genes: USH2A, GPR98, and DFNB31.

USH2 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 USH2. However, the risk to have a child affected with USH2 is increased. Testing of reproductive partners is recommended for carriers of USH2.

Usher syndrome is estimated to occur in approximately 3 to 6 per 100,000 newborns in Northern Europe and at least 4 in100,000 newborns in the general US population. Usher syndrome is divided into three major types, I, II, and III. Type II is thought to be the most common, accounting for over half of all cases. It is estimated that USH2 occurs in approximately 2 in 100,000 newborns in Denmark.

Genetics Home Reference: Usher syndrome (http://ghr.nlm.nih.gov/)
Genetic Alliance: Usher syndrome (http://www.diseaseinfosearch.org/)
Foundation fighting for blindness (https://www.blindness.org/)

OMIM [USH2A: 276901] (http://www.ncbi.nlm.nih.gov/omim)
Gene Reviews: Usher syndrome type II (http://www.ncbi.nlm.nih.gov/books/NBK1116/)

• Full gene sequencing