Identification of a novel RPGR mutation associated with X-linked cone-rod dystrophy in a Chinese family

A novel microdeletion of 517 kb downstream of the PAX6 gene in a Chinese family with congenital aniridia

BACKGROUND

To identify the disease-causing gene in a Chinese family affected with congenital aniridia.

METHODS

Patients underwent systematic ophthalmic examinations such as anterior segment photography, fundus photography, optical coherence tomography, and fundus fluorescein angiography. The proband was screened for pathogenic variants by whole exome sequencing (WES) and copy number variant (CNV) analysis. Real-time quantitative PCR (RT-qPCR) was applied to confirm the CNV results. Breakpoints were identified by long-range PCR followed by Sanger sequencing.

RESULTS

All seven members of this Chinese family, including four patients and three normal individuals, were recruited for this study. All patients showed bilateral congenital aniridia with nystagmus, except the son of the proband, who presented with bilateral partial coloboma of the iris. A novel heterozygous deletion (chr11:31,139,019-31,655,997) containing the 3' regulatory enhancers of the PAX6 gene was detected in this family. We also reviewed the reported microdeletions downstream of PAX6 in patients with aniridia.

CONCLUSIONS

We identified a novel microdeletion, 517 kb in size located about 133 kb downstream of the PAX6 gene, responsible for congenital aniridia in this Chinese family, which expands the spectrum of aniridia-associated mutations in PAX6.

Retinal degeneration in rpgra mutant zebrafish

Introduction: Pathogenic mutations in RPGR ^ORF15, one of two major human RPGR isoforms, were responsible for most X-linked retinitis pigmentosa cases. Previous studies have shown that RPGR plays a critical role in ciliary protein transport. However, the precise mechanisms of disease triggered by RPGR ^ORF15 mutations have yet to be clearly defined. There are two homologous genes in zebrafish, rpgra and rpgrb. Zebrafish rpgra has a single transcript homologous to human RPGR ^ORF15; rpgrb has two major transcripts: rpgrb ^ex1-17 and rpgrb ^ORF15, similar to human RPGR ^ex1-19 and RPGR ^ORF15, respectively. rpgrb knockdown in zebrafish resulted in both abnormal development and increased cell death in the dysplastic retina. However, the impact of knocking down rpgra in zebrafish remains undetermined. Here, we constructed a rpgra mutant zebrafish model to investigate the retina defect and related molecular mechanism. Methods: we utilized transcription activator-like effector nuclease (TALEN) to generate a rpgra mutant zebrafish. Western blot was used to determine protein expression. RT-PCR was used to quantify gene transcription levels. The visual function of embryonic zebrafish was detected by electroretinography. Immunohistochemistry was used to observe the pathological changes in the retina of mutant zebrafish and transmission electron microscope was employed to view subcellular structure of photoreceptor cells. Results: A homozygous rpgra mutant zebrafish with c.1675_1678delins21 mutation was successfully constructed. Despite the normal morphological development of the retina at 5 days post-fertilization, visual dysfunction was observed in the mutant zebrafish. Further histological and immunofluorescence assays indicated that rpgra mutant zebrafish retina photoreceptors progressively began to degenerate at 3-6 months. Additionally, the mislocalization of cone outer segment proteins (Opn1lw and Gnb3) and the accumulation of vacuole-like structures around the connecting cilium below the OSs were observed in mutant zebrafish. Furthermore, Rab8a, a key regulator of opsin-carrier vesicle trafficking, exhibited decreased expression and evident mislocalization in mutant zebrafish. Discussion: This study generated a novel rpgra mutant zebrafish model, which showed retinal degeneration. our data suggested Rpgra is necessary for the ciliary transport of cone-associated proteins, and further investigation is required to determine its function in rods. The rpgra mutant zebrafish constructed in this study may help us gain a better understanding of the molecular mechanism of retinal degeneration caused by RPGR ^ORF15 mutation and find some useful treatment in the future.