Targeted next-generation sequencing reveals novel USH2A mutations associated with diverse disease phenotypes: implications for clinical and molecular diagnosis.

Xue Chen,Chen Zhao,Xiaoxing Liu,Shaoping Ha,Kanxing Zhao,Weining Rong,Xiaoli Kang,Xunlun Sheng,Wenzhou Liu,Huiping Li,Yani Liu,Bart Dermaut

doi:10.1371/journal.pone.0105439

Abstract

USH2A mutations have been implicated in the disease etiology of several inherited diseases, including Usher syndrome type 2 (USH2), nonsyndromic retinitis pigmentosa (RP), and nonsyndromic deafness. The complex genetic and phenotypic spectrums relevant to USH2A defects make it difficult to manage patients with such mutations. In the present study, we aim to determine the genetic etiology and to characterize the correlated clinical phenotypes for three Chinese pedigrees with nonsyndromic RP, one with RP sine pigmento (RPSP), and one with USH2. Family histories and clinical details for all included patients were reviewed. Ophthalmic examinations included best corrected visual acuities, visual field measurements, funduscopy, and electroretinography. Targeted next-generation sequencing (NGS) was applied using two sequence capture arrays to reveal the disease causative mutations for each family. Genotype-phenotype correlations were also annotated. Seven USH2A mutations, including four missense substitutions (p.P2762A, p.G3320C, p.R3719H, and p.G4763R), two splice site variants (c.8223+1G>A and c.8559-2T>C), and a nonsense mutation (p.Y3745*), were identified as disease causative in the five investigated families, of which three reported to have consanguineous marriage. Among all seven mutations, six were novel, and one was recurrent. Two homozygous missense mutations (p.P2762A and p.G3320C) were found in one individual family suggesting a potential double hit effect. Significant phenotypic divergences were revealed among the five families. Three families of the five families were affected with early, moderated, or late onset RP, one with RPSP, and the other one with USH2. Our study expands the genotypic and phenotypic variability relevant to USH2A mutations, which would help with a clear insight into the complex genetic and phenotypic spectrums relevant to USH2A defects, and is complementary for a better management of patients with such mutations. We have also demonstrated that a targeted NGS approach is a valuable tool for the genetic diagnosis of USH2 and RP.

Highlights

Inherited retinal dystrophies (IRDs) comprise a group of monogenic diseases presenting significant clinical and genetic heterogeneities
Targeted nextgeneration sequencing (NGS) Approach Seven affected patients from five individual families were included in the present study with their ophthalmic and syndromic evaluations detailed in Figure 2 and Table 1
5, 7, 5, 1, and 11 variations were retained for patients ARRP01-IV:4, ARRP02-II:3, ARRP03-IV:3, ARRP04-IV:4, and SU01-II:2, respectively (Table 2)

Summary

Introduction

Inherited retinal dystrophies (IRDs) comprise a group of monogenic diseases presenting significant clinical and genetic heterogeneities. Patients affected with RP may manifest great varieties in the disease course, and RP presentations can overlay with other forms of IRDs, making it more difficult to obtain better clinical diagnoses for these patients. RP, usually a monogenic disorder, demonstrates all three types of mendelian inheritance modes, including autosomal dominant, autosomal recessive, and X-linked patterns. Targeted nextgeneration sequencing (NGS) strategies show significant improvements when compared with traditional detection approaches. It is more effective, cost-effective, and provides high sequencing accuracy. A targeted panel of known IRDs causative genes would help to obtain a potential molecular diagnosis for 50–70% of IRDs cases [4]

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Conclusion