A growing number of studies have shown that the total loss of function of the USH2A protein predisposes patients to Usher syndrome type IIa but that remnant protein function can lead to RP with or without hearing loss, indicating that mutations in the USH2A gene are relatively less harmful in nonsyndromic RP than in Usher syndrome type IIa. This evidence concerns the gene USH2A and Usher syndrome type 2A.