A novel C8orf37 splice mutation and genotype-phenotype correlation for cone-rod dystrophy

Background: To identify the disease-causing mutation in a consanguineous family of Morrocan origin with syndromic autosomal recessive (ar) cone-rod dystrophy (CRD) in two patients and describe genotype-phenotype correlations.

Materials and Methods: Genome-wide homozygosity mapping and direct sequencing of C8orf37, located in a homozygous interval, was performed in the family. mRNA analysis revealed the effect of the newly identified splice-site mutation. For a comparative analysis phenotypic and genetic data of C8orf37 mutations were extracted from published cases.

Results: The new splice-site mutation c.155+2T>C identified in the family results in a skipping of 82 bp. The CRD phenotypes of our patients were consistent with previous reports. Non-ocular findings in our patients and two previously described patients were postaxial polydactyly present at birth. Both families with additional postaxial polydactyly had splice site mutations affecting intron 1 of C8orf37, one at the slice donor and one at the splice acceptor site.

Conclusions: This report extends the genotypic spectrum of C8orf37-associated retinal dystrophies and demonstrates for the first time a genotype-phenotype correlation between an arCRD-polydactyly-association and truncating germline mutations affecting the N-terminal region of the protein. Furthermore, our findings underline the ciliary function of C8orf37 protein.     

Novel C8orf37 Mutations in Patients with Early-onset Retinal Dystrophy,Macular Atrophy,Cataracts, and High Myopia

Purpose: More than 50 genes are reported as causative genes of autosomal recessive (ar) retinitis pigmentosa (RP) and cone-rod dystrophy (CRD). It is challenging to identify causative mutations for arRP and arCRD. The purpose of the present study was to investigate clinical and genetic features of two siblings with early-onset retinal dystrophy.

Methods: Whole-exome sequencing was conducted for the two affected siblings and their unaffected brother and mother from a Japanese family. We performed complete ophthalmic examinations, including visual acuity, funduscopy, visual-field testing, electroretinography and optical coherence tomography.

Results: Whole-exome sequencing analysis identified novel compound heterozygous mutations, a splice site mutation (c.374?+?2T?>?C in intron 4) and a deletion mutation (c.575delC [p.T192MfsX28] in exon 6) of chromosome 8 open reading frame 37 (C8orf37) gene, which encodes a ciliary protein, in both patients. The mother carried the truncating mutation, and the brother carried neither mutation. Ophthalmic examinations revealed diffuse retinal degeneration, macular atrophy, non-recordable electroretinography responses, cataracts, and high myopia in both patients, who could not be diagnosed with either RP or CRD because of the severe retinal degeneration and early onset disease. Longitudinal follow-up of the patients revealed highly progressive retinal degeneration, macular atrophy, and visual field loss.

Conclusions: Recessive C8orf37 mutations have been identified in early to adolescent-onset arRP and arCRD with macular involvement. Our study identified two novel truncating mutations of the C8orf37 gene in siblings with early-onset retinal dystrophy, macular atrophy, cataracts, and high myopia.     

Efficacy of topical brinzolamide in children with retinal dystrophies

ABSTRACT

Background: Inherited retinal dystrophies are a leading cause of irreversible blindness in children in the United States. Topical carbonic anhydrase inhibitors have improved central vision and cystoid macular edema in patients with retinal dystrophies, but few studies have assessed their efficacy in children.

Materials and Methods: A retrospective chart review was performed with Institutional Review Board approval to identify pediatric patients with inherited retinal dystrophies who received topical brinzolamide at a single university center between 2008 and 2015. Serial visual acuity and central macular thicknesses were compared to assess the efficacy of brinzolamide.

Results: Seven subjects were identified who met the inclusion criteria. Four had juvenile X-linked retinoschisis, two had retinitis pigmentosa, and one had Leber congenital amaurosis. All were prescribed brinzolamide thrice daily; however, one patient was completely non-compliant. Four of the six treated patients exhibited a mild decrease in central macular thickness in both eyes during the study with all six treated patients having significantly improved vision at the first endpoint, 33.2 ± 8.2 months after treatment initiation. For treated patients, average visual acuity (LogMAR) ± standard error of the mean improved from 0.5 ± 0.04 pre-treatment to 0.3 ± 0.1 at the second endpoint, 50.2 ± 7.3 months after treatment initiation.

Conclusions: Mild anatomic improvement of macular cysts was seen in pediatric patients using brinzolamide. Visual acuity improvement occurred even without significant reduction in macular cysts. Further studies are needed to determine whether the beneficial effects of carbonic anhydrase inhibitors are sustained in children with inherited retinal degenerations.