Screening of a Large Cohort of L eber Congenital Amaurosis and Retinitis Pigmentosa Patients Identifies Novel LCA 5 Mutations and New Genotype–Phenotype Correlations

Abstract

This study was undertaken to investigate the prevalence of sequence variants in LCA 5 in patients with L eber congenital amaurosis ( LCA ), early‐onset retinal dystrophy ( EORD ), and autosomal recessive retinitis pigmentosa (ar RP ); to delineate the ocular phenotypes; and to provide an overview of all published LCA 5 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 were possible. DNA samples from 797 unrelated patients with LCA and 211 with the various types of retinitis pigmentosa ( RP ) were screened by S anger sequence analysis of all LCA 5 exons and intron/exon junctions. Some LCA patients were prescreened 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 LCA 5 variants were collected, amended for their correct nomenclature, and listed in a L eiden O pen V ariation D atabase ( LOVD ). Sequence analysis identified 18 new probands with 19 different LCA 5 variants. Seventeen of the 19 LCA 5 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 LCA 5 variants, the phenotype was more compatible with EORD with affected individuals displaying preserved islands of retinal pigment epithelium. One of the families with a milder phenotype 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 LCA 5 study to date. We sequenced 1,008 patients (797 with LCA , 211 with ar RP ) and identified 18 probands with LCA 5 mutations. Mutations in LCA 5 are a rare cause of childhood retinal dystrophy accounting for ∼2% of disease in this cohort, and the majority of LCA 5 mutations are likely null. The LCA 5 protein truncating mutations are predominantly associated with LCA . However, in two families with the milder EORD , the LCA 5 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. With an international LCA5 consortium, our goal was to identify LCA and RP patients with LCA5 mutations in preparation for a phase 1 clinical trial to test LCA5 gene replacement. This effort was successful in identifying 18 new LCA patients, novel mutations, and intact foveal cones, boding well for our trial.