A leaing cause of deaf-blindness, Usher syndrome (sometimes referred to as "Usher's syndrome") is a relatively rare genetic disorder that is associated with a mutation in any one of 10 genes. Other names for Usher syndrome include Hallgren syndrome, Usher-Hallgren syndrome, rp-dysacusis syndrome and dystrophia retinae dysacusis syndrome. Usher syndrome is incurable at present; however, using gene therapy to replace the missing gene, researchers have succeeded in reversing one form of the disease in knockout mice.