RESUMO
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.
Assuntos
Alelos , Proteínas de Ciclo Celular/genética , Distrofias de Cones e Bastonetes/genética , Mutação da Fase de Leitura/genética , Perda Auditiva Neurossensorial/genética , Deleção de Sequência/genética , Adulto , Autoantígenos/genética , Autoantígenos/metabolismo , Proteínas de Ciclo Celular/metabolismo , Criança , Distrofias de Cones e Bastonetes/fisiopatologia , Éxons/genética , Perda Auditiva Neurossensorial/fisiopatologia , Homozigoto , Humanos , RNA Mensageiro/análise , RNA Mensageiro/genética , Células Fotorreceptoras Retinianas Cones/metabolismo , Células Fotorreceptoras Retinianas Bastonetes/metabolismo , Síndromes de Usher/genética , Síndromes de Usher/metabolismo , Adulto JovemRESUMO
Genetic analysis of clinical phenotypes in consanguineous families is complicated by coinheritance of large DNA regions carrying independent variants. Here, we characterized a family with early onset cone-rod dystrophy (CRD) and muscular dystrophy. Homozygosity mapping (HM) followed by whole exome sequencing revealed a nonsense mutation, p.R270*, in ALMS1 and two novel potentially disease-causing missense variants, p.R1581C and p.Y2070C, in DYSF. ALMS1 and DYSF are genetically and physically linked on chromosome 2 in a genomic region suggested by HM and associated with Alström syndrome, which includes CRD, and with limb girdle muscular dystrophy, respectively. Affected family members lack additional systemic manifestations of Alström syndrome but exhibit mild muscular dystrophy. RNA-seq data did not reveal any significant variations in ALMS1 transcripts in the human retina. Our study thus implicates ALMS1 as a nonsyndromic retinal disease gene and suggests a potential role of variants in interacting cilia genes in modifying clinical phenotypes.
Assuntos
Consanguinidade , Proteínas de Membrana/genética , Proteínas Musculares/genética , Distrofia Muscular do Cíngulo dos Membros/genética , Mutação , Proteínas/genética , Retinose Pigmentar/genética , Proteínas de Ciclo Celular , Análise Mutacional de DNA , Disferlina , Feminino , Estudos de Associação Genética , Humanos , Masculino , Músculo Esquelético/metabolismo , Músculo Esquelético/patologia , Distrofia Muscular do Cíngulo dos Membros/diagnóstico , Linhagem , Fenótipo , Retina/patologia , Retinose Pigmentar/diagnósticoRESUMO
PURPOSE: The Israeli population has a unique genetic make-up, with a high prevalence of consanguineous marriages and autosomal recessive diseases. In rod-dominated phenotypes, disease-causing genes and mutations that differ from those identified in other populations often are incurred. We used whole exome sequencing (WES) to identify genetic defects in Israeli families with cone-dominated retinal phenotypes. METHODS: Clinical analysis included family history, detailed ocular examination, visual function testing, and retinal imaging. Whole exome sequencing, followed by segregation analysis, was performed in 6 cone-dominated retinopathy families in which prior mutation analysis did not reveal the causative gene. Based on the WES findings, we screened 106 additional families with cone-dominated phenotypes. RESULTS: The WES analysis revealed mutations in known retinopathy genes in five of the six families: two pathogenic mutations in the GUCY2D gene in three families, and one each in CDHR1 and C8orf37. Targeted screening of additional cone-dominated families led to identification of GUCY2D mutations in four other families, which included two highly probable novel disease-causing variants. CONCLUSIONS: Our study suggested that GUCY2D is a major cause of autosomal dominant cone and cone-rod dystrophies in Israel; this is similar to other Caucasian populations and is in contrast with retinitis pigmentosa (primary rod disease), where the genetic make-up of the Israeli population is distinct from other ethnic groups. We also conclude that WES permits more comprehensive and rapid analyses that can be followed by targeted screens of larger samples to delineate the genetic structure of retinal disease in unique population cohorts.