Xue Chen1,*, Xunlun Sheng2,*, Xiantao Sun3,*, Yuxin Zhang1, Chao Jiang1, Huiping Li2, Sijia Ding1, Yani Liu2, Wenzhou Liu2, Zili Li2 & Chen Zhao1,4

We aim to characterize the clinical features and genetic causes for two affected siblings from a Chinese family with cone dystrophy (CD). Two patients and four unaffected family members were recruited and received complete ophthalmic examinations. Genomic DNA was isolated from the peripheral blood samples from all patients. Targeted next-generation sequencing (NGS) approach followed by intrafamilal cosegregation and in silico analyses were employed to determine the genetic defects. Ophthalmic evaluations finalized the clinical diagnosis of CD for the two patients in this family, both of whom presented macular atrophy with no remarkable changes in the peripheral retina. Comprehensive genetic screening approach revealed biallelic missense mutations in the Leber congenital amaurosis 5 (LCA5) gene, p.[Ala212Pro];[Tyr441Cys], as disease causative for this family. Both mutations were novel. The first substitution was predicted to eliminate a hydrogen bond and alter the tertiary structure of lebercilin, protein encoded by LCA5. We for the first time report novel biallelic LCA5 mutations in causing CD. Our study extends the phenotypic and genotypic spectrums for LCA5-associated retinopathies and better illustrates its genotype-phenotype correlations, which would help with better genetic diagnosis, prognosis, and personalized treatment for CD patients.

Anneke I. den Hollander a, Ronald Roepman a, Robert K. Koenekoop b,!!, Frans P.M. Cremers a,! a Department of Human Genetics & Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands b McGill Ocular Genetics Laboratory, McGill University Health Centre, Montreal, Quebec, Canada H3H 1P3

a b s t r a c t

Leber congenital amaurosis (LCA) is the most severe retinal dystrophy causing blindness or severe visual impairment before the age of 1 year. Linkage analysis, homozygosity mapping and candidate gene analysis facilitated the identification of 14 genes mutated in patients with LCA and juvenile retinal degeneration, which together explain approximately 70% of the cases. Several of these genes have also been implicated in other non-syndromic or syndromic retinal diseases, such as retinitis pigmentosa and Joubert syndrome, respectively. CEP290 (15%), GUCY2D (12%), and CRB1 (10%) are the most frequently mutated LCA genes; one intronic CEP290 mutation (p.Cys998X) is found in !20% of all LCA patients from north-western Europe, although this frequency is lower in other populations. Despite the large degree of genetic and allelic heterogeneity, it is possible to identify the causative mutations in !55% of LCA patients by employing a microarray-based, allele-specific primer extension analysis of all known DNA variants. The LCA genes encode proteins with a wide variety of retinal functions, such as photoreceptor morphogenesis (CRB1, CRX), phototransduction (AIPL1, GUCY2D), vitamin A cycling (LRAT, RDH12, RPE65), guanine synthesis (IMPDH1), and outer segment phagocytosis (MERTK). Recently, several defects were identified that are likely to affect intra-photoreceptor ciliary transport processes (CEP290, LCA5, RPGRIP1, TULP1). As the eye represents an accessible and immune-privileged organ, it appears to be uniquely suitable for human gene replacement therapy. Rodent (Crb1, Lrat, Mertk, Rpe65, Rpgrip1), avian (Gucy2D) and canine (Rpe65) models for LCA and profound visual impairment have been successfully corrected employing adeno-associated virus or lentivirus-based gene therapy. Moreover, phase 1 clinical trials have been carried out in humans with RPE65 deficiencies. Apart from ethical considerations inherently linked to treating children, major obstacles for the treatment of LCA could be the putative developmental deficiencies in the visual cortex in persons blind from birth (amblyopia), the absence of sufficient numbers of viable photoreceptor or RPE cells in LCA patients, and the unknown and possibly toxic effects of overexpression of transduced genes. Future LCA research will focus on the identification of the remaining causal genes, the elucidation of the molecular mechanisms of disease in the retina, and the development of gene therapy approaches for different genetic subtypes of LCA.

Neruban Kumaran,1,2 Anthony T Moore,1,2,3 Richard G Weleber,4 Michel Michaelides1,2

Abstract

Leber congenital amaurosis (LCA) and early-onset severe retinal dystrophy (EOSRD) are both genetically and phenotypically heterogeneous, and characterised clinically by severe congenital/early infancy visual loss, nystagmus, amaurotic pupils and markedly reduced/ absent full-field electroretinograms. The vast genetic heterogeneity of inherited retinal disease has been established over the last 10 - 20 years, with diseasecausing variants identified in 25 genes to date associated with LCA/EOSRD, accounting for 70–80% of cases, with thereby more genes yet to be identified. There is now far greater understanding of the structural and functional associations seen in the various LCA/EOSRD genotypes. Subsequent development/characterisation of LCA/EOSRD animal models has shed light on the underlying pathogenesis and allowed the demonstration of successful rescue with gene replacement therapy and pharmacological intervention in multiple models. These advancements have culminated in more than 12 completed, ongoing and anticipated phase I/II and phase III gene therapy and pharmacological human clinical trials. This review describes the clinical and genetic characteristics of LCA/EOSRD and the differential diagnoses to be considered. We discuss in further detail the diagnostic clinical features, pathophysiology, animal models and human treatment studies and trials, in the more common genetic subtypes and/or those closest to intervention.