Screening of a Large Cohort of Leber Congenital Amaurosis and Retinitis Pigmentosa Patients Identifies Novel LCA5 Mutations and New Genotype-Phenotype Correlations

Abstract

To investigate the prevalence of sequence variants in LCA5 in patients with Leber congenital amaurosis (LCA), early onset rod-cone dystrophy (EORD) and autosomal recessive retinitis pigmentosa (RP), to delineate the ocular phenotypes, and to provide an overview of all published LCA5 variants in an online database._Patients underwent standard ophthalmic evaluations after providing informed consent. In selected patients, optical coherence tomography (OCT) and fundus autofluorescence imaging was possible. DNA samples from 797 unrelated patients with LCA and 211 with the various types of RP were screened by Sanger sequence analysis of all LCA5 exons and intron/exon junctions. Some LCA patients were pre-screened by APEX technology or selected based on homozygosity mapping. In silico analyses were performed to assess the pathogenicity of the variants. Segregation analysis was performed where possible. Published and novel LCA5 variants were collected, amended for their correct nomenclature, and listed in a Leiden Open Variation Database (LOVD). Sequence analysis identified 18 new probands with 19 different LCA5 variants. Seventeen of the 19 LCA5 variants were novel. Except for two missense variants and one splice site variant, all variants were protein-truncating mutations. Most patients expressed a severe phenotype, typical of LCA. However, some LCA subjects had better vision and intact inner segment/outer segment (IS/OS) junctions on OCT imaging. In two families with LCA5 variants, the phenotype was more compatible with EORD with affected individuals displaying preserved islands of RPE. One of these milder families harbored a homozygous splice site mutation, a second family was found to have a combination of a stop mutation and a missense mutation. This is the largest LCA5 study to date. We sequenced 1008 patients (797 with LCA, 211 with arRP) and identified 18 probands with LCA5 mutations. Mutations in LCA5 are a rare cause of childhood retinal dystrophy accounting for ~2% of disease in this cohort and the majority of LCA5 mutations are likely null. The LCA5 protein truncating mutations are predominantly associated with LCA. However, in two families with the milder EORD, the LCA5 gene analysis revealed a homozygous splice site mutation in one and a stop mutation in combination with a missense mutation in a second family, suggesting that this milder phenotype is due to residual function of lebercilin and expanding the currently known phenotypic spectrum to include the milder early onset RP. Some patients have remaining foveal cone structures (intact IS/OS junctions on OCT imaging) and remaining visual acuities, which may bode well for upcoming treatment trials.

Next-generation sequencing applied to a large French cone and cone-rod dystrophy cohort: mutation spectrum and new genotype-phenotype correlation

“…Braun and co-workers were first to provide evidence for the possibility of intronic variants near rare alternate splice junctions that could be pathogenic by increasing the probability of mis-splicing at these sites [65]. Deep intronic mutations leading to truncated proteins have also been described in Usher syndrome and LCA [66, 67]. This need to be further investigated in our 6 patients.…”

The genetic profile of Leber congenital amaurosis in an Australian cohort

“…The mutant protein is predicted to lose part of exon 7 and all of exon 8. There are four other reported examples of PTCs occurring after c.1191 (Boldt et al 2011;Mackay et al 2013;Wang et al 2015) in the Human Gene Mutation Database (HGMD) (Stenson et al 2014). The siblings were diagnosed with fundus albipunctatus and cone-rod dystrophy, with the latter associated with light perception (LP) since birth, Franceschetti's oculodigital sign and keratoconus (Table S4).…”

RDH12Mutations Cause a Severe Retinal Degeneration With Relatively Spared Rod Function

“…edu/retnet/disease.htm, available in the public domain). [4][5][6][7] Mutations in the retinol dehydrogenase 12 gene (RDH12), which maps to a locus on chromosome 14 (14q23.3-24.1) known as LCA13, accounts for about 4% of all autosomal recessive LCA, a disease that affects about 20% of all children that attend schools for the blind. 1,4,8,9 The gene encodes a protein member of the family of retinol dehydrogenases that localizes to the photoreceptor inner segment of rods and cones.…”