How many types of Usher syndrome are there?
There are three clinical types of Usher Syndrome:
Type 1 – causes profound deafness. Vision loss cause by retinitis pigmentosa (RP) may be noticed before the age of 10. Poor balance is often associated with Usher type 1, which causes delay in the age of sitting and walking. Many adults with Usher 1 communicate with sign language and identify as a culturally Deaf. Children with Usher type 1 who receive cochlear implants at an early age usually communicate using speech and lip-reading.
Type 2 – causes a moderate hearing loss. RP may not become apparent until adolescence. Speech assisted by the use of lip-reading and hearing aids will usually be their primary method of communication. Balance is not affected.
Type 3 – is the rarest form of Usher syndrome. It occurs with higher frequency in people of Ashkenazi Jewish and Finnish ancestry. Children usually have normal hearing and sight at birth, then develop hearing loss and RP in adolescence or later. Hearing can deteriorate steadily over ten or fifteen years. Some with type 3 also experience balance problems.
There are at least eleven different genetic types of Usher syndrome, as determined by the genes that are involved. There are six different genes that cause Usher type 1, three that cause Usher type 2, and two that cause Usher type 3. One cannot determine the genetic type by clinical testing; DNA testing is the only reliable way of determining the true genetic type.
Individuals with Usher type 1 are typically profoundly deaf whereas those with type 2 are usually hard of hearing. People with Usher type 1 also experience balance problems from birth. This causes them to usually start walking later than their peers. Children with type 2 walk at the typical age of 10 to 14 months. The RP of Usher type I is often diagnosed earlier that that for type 2, though recent breakthroughs in genetic testing are allowing for earlier diagnosis of all types of Usher syndrome