Bi-allelic Truncating Mutations in CEP78, Encoding Centrosomal Protein 78, Cause Cone-Rod Degeneration with Sensorineural Hearing Loss.

Inherited retinal diseases (IRDs) are a diverse group of genetically and clinically heterogeneous retinal abnormalities. The present study was designed to identify genetic defects in individuals with an uncommon combination of autosomal recessive progressive cone-rod degeneration accompanied by sensorineural hearing loss (arCRD-SNHL). Homozygosity mapping followed by whole-exome sequencing (WES) and founder mutation screening revealed two truncating rare variants (c.893-1G>A and c.534delT) in CEP78, which encodes centrosomal protein 78, in six individuals of Jewish ancestry with CRD and SNHL. RT-PCR analysis of CEP78 in blood leukocytes of affected individuals revealed that the c.893-1G>A mutation causes exon 7 skipping leading to deletion of 65bp, predicted to result in a frameshift and therefore a truncated protein (p.Asp298Valfs(∗)17). RT-PCR analysis of 17 human tissues demonstrated ubiquitous expression of different CEP78 transcripts. RNA-seq analysis revealed three transcripts in the human retina and relatively higher expression in S-cone-like photoreceptors of Nrl-knockout retina compared to rods. Immunohistochemistry studies in the human retina showed intense labeling of cone inner segments compared to rods. CEP78 was reported previously to interact with c-nap1, encoded by CEP250 that we reported earlier to cause atypical Usher syndrome. We conclude that truncating mutations in CEP78 result in a phenotype involving both the visual and auditory systems but different from typical Usher syndrome.

Mutations in IMPG2, encoding interphotoreceptor matrix proteoglycan 2, cause autosomal-recessive retinitis pigmentosa.

Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal diseases caused by progressive degeneration of the photoreceptor cells. Using autozygosity mapping, we identified two families, each with three affected siblings sharing large overlapping homozygous regions that harbored the IMPG2 gene on chromosome 3. Sequence analysis of IMPG2 in the two index cases revealed homozygous mutations cosegregating with the disease in the respective families: three affected siblings of Iraqi Jewish ancestry displayed a nonsense mutation, and a Dutch family displayed a 1.8 kb genomic deletion that removes exon 9 and results in the absence of seven amino acids in a conserved SEA domain of the IMPG2 protein. Transient transfection of COS-1 cells showed that a construct expressing the wild-type SEA domain is properly targeted to the plasma membrane, whereas the mutant lacking the seven amino acids appears to be retained in the endoplasmic reticulum. Mutation analysis in ten additional index cases that were of Dutch, Israeli, Italian, and Pakistani origin and had homozygous regions encompassing IMPG2 revealed five additional mutations; four nonsense mutations and one missense mutation affecting a highly conserved phenylalanine residue. Most patients with IMPG2 mutations showed an early-onset form of RP with progressive visual-field loss and deterioration of visual acuity. The patient with the missense mutation, however, was diagnosed with maculopathy. The IMPG2 gene encodes the interphotoreceptor matrix proteoglycan IMPG2, which is a constituent of the interphotoreceptor matrix. Our data therefore show that mutations in a structural component of the interphotoreceptor matrix can cause arRP.

A homozygous frameshift mutation in BEST1 causes the classical form of Best disease in an autosomal recessive mode.

PURPOSE: Best disease is a monogenic macular degeneration caused mainly by heterozygous mutations in the BEST1 gene. The objective was to characterize the molecular and clinical features of patients with the classical form of Best disease that is inherited in an autosomal recessive mode. METHODS: Clinical evaluation included detailed family history, a full ophthalmologic examination, electro-oculography (EOG), electroretinography, color vision testing, and ocular imaging. Mutation analysis was performed by direct sequencing of PCR products. RESULTS: Two young siblings affected by Best disease, as confirmed by funduscopy, retinal imaging, and electrophysiologic assessment, were recruited for the study. Molecular analysis revealed a novel homozygous deletion (c.1415delT) in the BEST1 gene leading to a frameshift followed by a premature stop codon, which cosegregated with the disease in a recessive mode. The heterozygous parents had normal visual acuity, retinal appearance, and function. The two heterozygous grandmothers, ages 61 and 62, also had normal Arden ratios on EOG, but one of them manifested moderate-to-severe dry non-neovascular age-related macular degeneration. CONCLUSIONS: We show here that the typical vitelliform phenotype of Best disease, usually transmitted in an autosomal dominant fashion, can be inherited as an autosomal recessive disease due to homozygosity for a frameshift mutation.