A detailed clinical and molecular survey of subjects with nonsyndromic USH2A retinopathy reveals an allelic hierarchy of disease-causing variants.

Defects in USH2A cause both isolated retinal disease and Usher syndrome (ie, retinal disease and deafness). To gain insights into isolated/nonsyndromic USH2A retinopathy, we screened USH2A in 186 probands with recessive retinal disease and no hearing complaint in childhood (discovery cohort) and in 84 probands with recessive retinal disease (replication cohort). Detailed phenotyping, including retinal imaging and audiological assessment, was performed in individuals with two likely disease-causing USH2A variants. Further genetic testing, including screening for a deep-intronic disease-causing variant and large deletions/duplications, was performed in those with one likely disease-causing change. Overall, 23 of 186 probands (discovery cohort) were found to harbour two likely disease-causing variants in USH2A. Some of these variants were predominantly associated with nonsyndromic retinal degeneration ('retinal disease-specific'); these included the common c.2276 G>T, p.(Cys759Phe) mutation and five additional variants: c.2802 T>G, p.(Cys934Trp); c.10073 G>A, p.(Cys3358Tyr); c.11156 G>A, p.(Arg3719His); c.12295-3 T>A; and c.12575 G>A, p.(Arg4192His). An allelic hierarchy was observed in the discovery cohort and confirmed in the replication cohort. In nonsyndromic USH2A disease, retinopathy was consistent with retinitis pigmentosa and the audiological phenotype was variable. USH2A retinopathy is a common cause of nonsyndromic recessive retinal degeneration and has a different mutational spectrum to that observed in Usher syndrome. The following model is proposed: the presence of at least one 'retinal disease-specific' USH2A allele in a patient with USH2A-related disease results in the preservation of normal hearing. Careful genotype-phenotype studies such as this will become increasingly important, especially now that high-throughput sequencing is widely used in the clinical setting.European Journal of Human Genetics advance online publication, 4 February 2015; doi:10.1038/ejhg.2014.283

Comprehensive screening of the USH2A gene in Usher syndrome type II and non-syndromic recessive retinitis pigmentosa

A screen of the entire coding region of the USH2A gene in 129 unrelated patients with Usher syndrome type II (USH2) and in 146 unrelated patients with non-syndromic autosomal recessive retinitis pigmentosa (ARRP) uncovered 54 different sequence variations, including 18 likely pathogenic mutations (13 frameshift, three nonsense, and two missense), 12 changes of uncertain pathogenicity (11 missense changes and one in-frame deletion), and 24 non-pathogenic rare variants or polymorphisms. Of the 18 likely pathogenic mutations, nine were novel. Among the USH2 patients, 50 (39%) had one or two likely pathogenic mutations. The most common mutant allele in USH2 patients was E767fs, which was found in 29 patients, including one homozygote. Among the ARRP patients, we found 17 (12%) with one or two likely pathogenic mutations. The most common mutant allele in ARRP patients was C759F and it was found in 10 patients. The C759F allele was also found in two USH2 patients; in neither of them was a change in the other allele found. The second most common mutant allele in both patient groups was L1447fs (found in 6/50 USH2 patients and 6/17 ARRP patients). Of the 50+17=67 patients with identified USH2A mutations, only one mutation in one allele was found in 41+12=53 (79%); the reason for the high proportion of patients with only one identified mutation is obscure. Our results indicate that USH2A mutations are found in about 7% of all cases of RP in North America, a frequency similar to the RPGR gene (8%) and the rhodopsin gene (10%)