Identification of a novel RPGRIP1 mutation in an Iranian family with leber congenital amaurosis by exome sequencing

Abstract

Leber congenital amaurosis (LCA) is a heterogeneous, early-onset inherited retinal dystrophy, which is associated with severe visual impairment. We aimed to determine the disease-causing variants in Iranian LCA and evaluate the clinical implications. Clinically, a possible LCA disease was found through diagnostic imaging, such as fundus photography, autofluorescence and optical coherence tomography. All affected patients showed typical eye symptoms associated with LCA including narrow arterioles, blindness, pigmentary changes and nystagmus. Target exome sequencing was performed to analyse the proband DNA. A homozygous novel c. 2889delT (p.P963 fs) mutation in the RPGRIP1 gene was identified, which was likely the deleterious and pathogenic mutation in the proband. Structurally, this mutation lost a retinitis pigmentosa GTPase regulator (RPGR)-interacting domain at the C-terminus which most likely impaired stability in the RPGRIP1 with the distribution of polarised proteins in the cilium connecting process. Sanger sequencing showed complete co-segregation in this pedigree. This study provides compelling evidence that the c. 2889delT (p.P963 fs) mutation in the RPGRIP1 gene works as a pathogenic mutation that contributes to the progression of LCA.

Keywords: RPGRIP1; Iran; leber congenital amaurosis; mutation; target exome sequencing.

Figure 1

Schematic pedigrees showing in an arLCA family that is described in this study. Family number and disease‐causing mutation are noted in above pedigree. Normal individuals are shown as clear circles (females) and squares (males), affected individuals are shown as filled symbols, and carriers are shown as hemi‐filled symbols. The patient above the arrow indicates the proband (II: 1), where target exome sequencing was performed with deletion mutation of RPGRIP1:NM_020366:exon17:c.2889del.T:p.P963 fs.

Figure 2

Representative fundus photographs of patient II:1 (proband) from both eyes. Panel A.  14‐year‐old Iranian female patient. Panel B. Fundus photographs of unaffected age‐matched control. The comparison between two panels clearly has shown the ‘salt and pepper’ pigment mottling pattern, severe RPE atrophic changes and the transparent in the macula in the patient that is afflicted with the disease.

Figure 3

Retinal phenotypes of proband. Panel A. Optical coherence tomography and electroretinography features of inherited retinal dystrophies in left eye for II:1. Panel B. Representative optical coherence tomography and electroretinography left eye of control. This figure shows that the patient had marked thinning and disruption of the photoreceptor layer, choroid and the retinitis pigment epithelium.

Figure 4

Sanger sequencing validation. A, B, C, D and E indicate the sequencing results in II: 1, II: 2 (mutant homozygous type), I: 2, III: 2 (heterozygous type), N (wild type, normal control: a normal person from no eye disease history family), respectively. The arrows indicate the deletion at the nucleotide position NM_020366:exon17:c.2889del.T in RPGRIP1 gene.

Figure 5

Schematic diagram of the alignment scores for RPGRIP1 SNPs and protein amino acid residues, corresponding to the c.2889del.T:p.P963 fs. The highlighted amino acid residues in blue are conserved the same. The mutation position is shown in the grey box. The red line shows the alignment scores ≥200, the tiny black line shows the alignment scores ≤40, and the dashed line shows the totally deletion part, between the query of the mutations and wild type. ND, nuclear domain; C2‐N, N terminal of protein kinase C conserved domain 2; C2‐C, C‐terminal of protein kinase C conserved domain 2; CC, coiled‐coil domain; RID, RPGR‐interacting domain.

Figure 6

Flow chart showing an approach of this kind of study. Flow chart for genetic tests, selection of patients and WES system in the Iranian LCA family that was described in this study.