Retinitis pigmentosa (RP) is a retinal degenerative disease characterized by the progressive loss of photoreceptors. We have previously demonstrated that RP can be caused by recessive mutations in the human FAM161A gene, encoding a protein with unknown function that contains a conserved region shared only with a distant paralog, FAM161B. In this study, we show that FAM161A localizes at the base of the photoreceptor connecting cilium in human, mouse and rat. Furthermore, it is also present at the ciliary basal body in ciliated mammalian cells, both in native conditions and upon the expression of recombinant tagged proteins. Yeast two-hybrid analysis of binary interactions between FAM161A and an array of ciliary and ciliopathy-associated proteins reveals direct interaction with lebercilin, CEP290, OFD1 and SDCCAG8, all involved in hereditary retinal degeneration. These interactions are mediated by the C-terminal moiety of FAM161A, as demonstrated by pull-down experiments in cultured cell lines and in bovine retinal extracts. As other ciliary proteins, FAM161A can also interact with the microtubules and organize itself into microtubule-dependent intracellular networks. Moreover, small interfering RNA-mediated depletion of FAM161A transcripts in cultured cells causes the reduction in assembled primary cilia. Taken together, these data indicate that FAM161A-associated RP can be considered as a novel retinal ciliopathy and that its molecular pathogenesis may be related to other ciliopathies.
Purpose.: We evaluated the role of Crumbs homolog 1 (CRB1) in autosomal recessive (AR) retinal diseases in the Israeli and Palestinian populations using homozygosity mapping. Methods.: Clinical analysis included family history, ocular examination, full-field electroretinography (ERG), and funduscopy. Molecular analysis included homozygosity mapping using whole genome single nucleotide polymorphism (SNP) arrays and mutation analysis of CRB1. Results.: We recruited over 400 families with AR nonsyndromic retinal degenerations, including retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA). SNP array analysis was performed on 175 index cases, eight of whom carried a homozygous region on chromosome 1 harboring CRB1. A subsequent CRB1 mutation analysis of the eight families, followed by screening of candidate founder mutations in the whole cohort of patients, revealed a total of 13 mutations, six of which are novel, in 15 families. Nine mutations were family-specific, and four were founder mutations identified in patients of Arab-Muslim origin, and Jews originated from Iraq and Kurdistan. Interestingly, a null mutation on at least one of the two mutated CRB1 alleles results in the LCA diagnosis, whereas patients carrying missense mutations were diagnosed with either RP or LCA. The average age at which CRB1 patients were referred to ERG testing was young (11 years). Of the 30 identified CRB1 patients, five had Coats-like exudative vasculopathy. Conclusions.: Our data show that CRB1 mutations are a relatively frequent cause of AR early-onset retinal degeneration in the Israeli and Palestinian populations (10% of LCA families), and causes severe retinal degeneration at an early age.
Purpose: To identify mutations in FAM161A underlying autosomal recessive retinitis pigmentosa (arRP) in the Dutch and Belgian populations and to investigate whether common FAM161A-associated phenotypic features could be identified. Methods: Homozygosity mapping, amplification-refractory mutation system (ARMS) analysis, and Sanger sequencing were performed to identify mutations in FAM161A. Microsatellite and SNP markers were genotyped for haplotype analysis. Patients with biallelic mutations underwent detailed ophthalmologic examinations, including measuring best-corrected visual acuity, extensive fundus photography with reflectance and autofluorescence imaging, and optical coherence tomography. Results: Homozygosity mapping in 230 Dutch individuals with suspected arRP yielded five individuals with a homozygous region harboring FAM161A. Sanger sequencing revealed a homozygous nonsense mutation (c.1309A>T; p.[Arg437*]) in one individual. Subsequent ARMS analysis and Sanger sequencing in Dutch and Belgian arRP patients resulted in the identification of seven additional individuals carrying the p.(Arg437*) mutation, either homozygously or compound heterozygously with another mutation. Haplotype analysis identified a shared haplotype block of 409 kb surrounding the p.(Arg437*) mutation in all patients, suggesting a founder effect. Although the age of onset was variable among patients, all eight developed pronounced outer retinal loss with severe visual field defects and a bull's eye–like maculopathy, followed by loss of central vision within 2 decades after the initial diagnosis in five subjects. Conclusions: A founder mutation in FAM161A p.(Arg437*) underlies approximately 2% of arRP cases in the Dutch and Belgian populations. The age of onset of the retinal dystrophy appears variable, but progression can be steep, with almost complete loss of central vision later in life.
The Israeli and Palestinian populations are known to have a relatively high level of consanguineous marriages, leading to a relatively high frequency of autosomal recessive (AR) diseases. Our purpose was to use the homozygosity mapping approach, aiming to prioritize the set of genes and identify the molecular genetic causes underlying AR retinal degenerations in the Israeli and Palestinian populations.Clinical analysis included family history, ocular examination, full-field electroretinography (ERG), and funduscopy. Molecular analysis included homozygosity mapping and mutation analysis of candidate genes.We recruited for the study families with AR nonsyndromic retinal degenerations, including mainly retinitis pigmentosa (RP), cone-rod degeneration (CRD), and Leber congenital amaurosis (LCA). With the aim to identify the causative genes in these families, we performed homozygosity mapping using whole genome single nucleotide polymorphism (SNP) arrays in 125 families. The analysis revealed the identification of 14 mutations, 5 of which are novel, in 16 of the families. The mutations were identified in the following eight genes: RDH12, PROM1, MFRP, TULP1, LCA5, CEP290, NR2E3, and EYS. While most patients had a retinal disease that is compatible with the causing gene, in some cases new clinical features are evident.Homozygosity mapping is a powerful tool to identify genetic defects underlying heterogeneous AR disorders, such as RP and LCA, in consanguineous and nonconsanguineous patients. The identification of significant and large homozygous regions, which do not include any known retinal disease genes, may be a useful tool to identify novel disease-causing genes, using next generation sequencing.
