Identification of a novel homozygous nonsense mutation in EYS in a Chinese family with autosomal recessive retinitis pigmentosa

Abstract

Background: Retinitis pigmentosa is the most important hereditary retinal degenerative disease, which has a high degree of clinical and genetic heterogeneity. More than half of all cases of retinitis pigmentosa are autosomal recessive (arRP), but the gene(s) causing arRP in most families has yet to be identified. The purpose of this study is to identify the genetic basis of severe arRP in a consanguineous Chinese family.

Methods: Linkage and haplotype analyses were used to define the chromosomal location of the pathogenic gene in the Chinese arRP family. Direct DNA sequence analysis of the entire coding region and exon-intron boundaries of EYS was used to determine the disease-causing mutation, and to demonstrate that the mutation co-segregates with the disease in the family.

Results: A single nucleotide substitution of G to T at nucleotide 5506 of EYS was identified in the Chinese arRP family. This change caused a substitution of a glutamic acid residue at codon 1,836 by a stop codon TAA (p.E1836X), and resulted in a premature truncated EYS protein with 1,835 amino acids. Three affected siblings in the family were homozygous for the p.E1836X mutation, while the other unaffected family members carried one mutant allele and one normal EYS allele. The nonsense mutation p.E1836X was not detected in 200 unrelated normal controls.

Conclusions: The EYS gene is a recently identified disease-causing gene for retinitis pigmentosa, and encodes the orthologue of Drosophila spacemaker. To date, there are only eight mutations in EYS that have been identified to cause arRP. Here we report one novel homozygous nonsense mutation of EYS in a consanguineous Chinese arRP family. Our study represents the first independent confirmation that mutations in EYS cause arRP. Additionally, this is the first EYS mutation identified in the Chinese population.

Figure 1

Pedigree structure and haplotype analysis at the RP25 locus. Blackened bars indicate the disease haplotype. Filled squares or filled circles represent male or female individuals affected with RP, respectively. Arrow points to the proband (II2). All patients in the arRP family carry the homozygous haplotype between single nucleotide polymorphisms rs4710292 and rs4710437. The genomic positions of two markers are from Human (Homo sapiens) Genome Browser Gateway, the GRCh37 build version, and six SNPs are from NCBI B37.1 assembly.

Figure 2

Fundus photographs and ERG of the proband in the Chinese arRP family. The features of waxy-pale disc, arteriolar attenuation, and bone-spicule pigment deposit in the mid-peripheral retina are shown in A. The full-field ERG in the proband in B, either a-wave or b-wave has obvious reduced amplitude and prolonged response time in both eyes.

Figure 3

Identification of the homozygous mutation in the consanguineous Chinese arRP family. A and B show the exon 26 of EYS sequences from a normal individual and an affected individual with p.E1836X mutation, respectively. The sequence for individual III1, who is heterozygous for the mutation, is shown in C.