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 from birth is often associated with Usher type 1, which causes delays in sitting and walking. Children with Usher type 1 who receive cochlear implants at an early age usually communicate using speech and lip-reading. Many adults with Usher 1 communicate with sign language and identify as a culturally Deaf and/or DeafBlind.
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 or cochlear implants will usually be their primary method of communication. Balance is not affected, therefore children with type 2 walk at the typical age of 10 to 14 months.
Type 3 – is the rarest form of Usher syndrome. It occurs with higher frequency in individuals of Ashkenazi Jewish and Finnish heritage. Children usually have normal hearing and vision 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. There are six different genes that cause Usher type 1, three that cause Usher type 2, and two that cause Usher type 3. DNA testing - usually with a simple blood test - is the only reliable way of determining the true genetic type.
Recent breakthroughs in genetic testing are allowing for earlier diagnosis of all types of Usher syndrome.