How many people are affected by Usher syndrome ?
Usher syndrome is thought to be responsible for 3 percent to 6 percent of all childhood deafness and about 50 percent of deaf-blindness in adults. Usher syndrome type I is estimated to occur in at least 4 per 100,000 people. It may be more common in certain ethnic populations, such as people with Ashkenazi (central and eastern European) Jewish ancestry and the Acadian population in Louisiana. Type II is thought to be the most common form of Usher syndrome, although the frequency of this type is unknown. Type III Usher syndrome accounts for only a small percentage of all Usher syndrome cases in most populations. This form of the condition is more common in the Finnish population, however, where it accounts for about 40 percent of all cases.