Whole exome sequencing identifies a novel splice-site mutation in IMPG2 gene causing Stargardt-like juvenile macular dystrophy in a north Indian family.

We report on the genetic analysis of a north Indian family affected with Stargardt-like juvenile macular dystrophy. Considering an autosomal recessive inheritance of macular dystrophy in the recruited family, whole exome sequencing was employed in two affected siblings and their mother. We have identified a novel splice-site variant NC_000003.11(NM_016247.3):c.1239 + 1G > T, co-segregating in the affected siblings, in the Interphotoreceptor Matrix Proteoglycan 2 (IMPG2) gene. The identified variant is present immediately after exon 11, and is predicted to disrupt the wild-type donor splice-site of IMPG2 transcripts. We confirmed the splice-site changes in the IMPG2 transcripts using minigene functional assay. Although a number of studies on IMPG2 have demonstrated its involvement in retinitis pigmentosa and vitelliform macular dystrophy, this is the first report of a splice-site variant in IMPG2 that is responsible for Stargardt-like juvenile macular dystrophy.

Whole exome sequencing unveils a frameshift mutation in CNGB3 for cone dystrophy: A case report of an Indian family.

RATIONALE: Genetic elucidation of cone-dominated retinal dystrophies in Indian subcontinent is much needed to identify and catalog underlying genetic defects. In this context, the present study recruited a consanguineous Indian family affected with autosomal recessive cone dystrophy (CD). Considering the huge genetic heterogeneity and recessive inheritance of the disease, we chose to dissect out causal variant in this family by whole exome sequencing (WES). PATIENT CONCERNS: In the recruited family, three of the six siblings had complaints of poor visual acuity, photophobia, and disturbed colour vision since early childhood. Fundus examination disclosed vascular attenuation and macular retinal pigment epithelium (RPE) changes in all the affected siblings, signifying degeneration of photoreceptor cells. DIAGNOSIS: Complete clinical investigation and electroretinography studies led to the diagnosis of cone dystrophy in three siblings of the family. INTERVENTIONS: Detailed ophthalmic examination, including family history, visual function testing, and retinal imaging, was performed. We captured and sequenced exomes of 2 affected siblings and their mother using SureSelect Human All Exon V5 Kit on Illumina HiSeq 2000/2500 platform with 100 bp paired-end sequencing method. Candidates after data analysis were screened by segregation analysis and Sanger sequencing. Considering recessive inheritance and consanguinity in the pedigree, we attempted to map large loci homozygous by descent in the genome of patients using exome sequencing variants. Extensive protein modeling was carried out to assess possible consequences of the identified variant on the 3-dimensional structure of the protein. OUTCOMES: WES generated more than 65,000 variants for each individual. Assuming recessive inheritance, 13,026 variants were selected. Further filtering on the basis of their position in gene, class, and minor allele frequency constricted the huge list to 12 rare variants. Finally, we ascertained a single base deletion c.1148delC (p.Thr383fs) in the gene CNGB3 as the causal variant. This is a recurrent frameshift mutation resulting in truncated CNGB3 protein. We mapped a large 15-Mb stretch of homozygous markers spanning the causal variant in the proband. The gene CNGB3 encodes modulatory subunit of cyclic nucleotide-gated channels in cone photoreceptors. Protein modeling reveals loss of 2 transmembrane helices and conserved CAP_ED domain in truncated CNGB3, which eventually is predicted to form nonfunctional channels and hamper phototransduction. LESSONS: We have identified a recurrent mutation c.1148delC (p.Thr383fs) in CNGB3 for autosomal recessive CD. The present report provides the first description of CNGB3 mutation from India. It is also the foremost investigation of familial CD in Indian patients; therefore, it presents the primary genetic etiology of CD in India.

A new clinico-tomographic classification and management algorithm for Descemet's membrane detachment.

OBJECTIVE: To propose a new clinico-tomographic classification of Descemet's detachment (DD). METHODS: Interventional case series of 35 eyes with DD were clinico-tomographically classified as: (1)Rhegmatogenous DD (RDD)-lax, free floating DM secondary to DM tear/hole/dialysis; ASOCT showing undulating linear signal with total length equalling overlying stromal arc length. (2) Tractional DD (TDD)-foreshortened, taut DM with tractional/fibrotic component; ASOCT showing detached DM chord length less than overlying stromal arc length. (3) Bullous DD (BDD)-bulge of DM into AC in absence of DM break or needle puncture break too small to allow egress of contents; ASOCT showing convex signal. (4) Complex DD (CDD)-Complex variants and combinations seen clinically and on ASOCT. RESULTS: RDD was most common (n=23), 19 were RDD with tear (post-surgical) treated by observation(n=3)/pneumodescemetopexy(n=16), 2 were RDD with hole due to inadvertent DM perforation in deep anterior lamellar keratoplasty treated by pneumodescemetopexy and fibrin glue, 2 were RDD with dialysis post-Descemetorhexis in Descemet's Membrane Endothelial Keratoplasty, not requiring treatment. TDD (n=4) was treated by relaxing Descemetotomy (n=3) or EK (n=1, poor endothelium); BDD (n=3) with two improving spontaneously; CDD (n=5) treated by refloatation with air (n=3)/EK (n=1)/penetrating keratoplasty (n=1). CONCLUSION: Treatment and prognosis of DD varies based on etio-morphology. This classification allows systematic approach for diagnosis, management and prognostication.

A novel mutation in FRMD7 causes X-linked idiopathic congenital nystagmus in a North Indian family.

Idiopathic congenital nystagmus (ICN) is the most common form of oculomotor disorder characterized by involuntary bilateral ocular oscillations. Primarily the disease is an ocular anomaly but the pathophysiology is associated with neuronal cytoskeletal dynamics in the brain. In the current study, a three generation North Indian family affected with X-linked idiopathic congenital nystagmus (XLICN) was recruited. Our aim was to identify the causal mutation for ICN in the family by screening the candidate gene, FERM domain containing-7 (FRMD7). This gene has been implicated in XLICN as it regulates neuronal cytoskeletal proteins and neurite outgrowth in the developing brain. Therefore, the entire protein coding region, including splice junctions, 5' UTR and 3' UTR of FRMD7 was screened by PCR-Sanger sequencing. Targeted sequencing revealed a novel A to G transition in the exon seven (c.556A>G), resulting in a conservative substitution of methionine by valine at codon 186 (p.M186V). A cohort of healthy individuals was also checked for presence of the putative causal variant by allele specific PCR. All the affected males and carriers in the family shared this variant; however, this was absent in the unaffected males as well as 100 unrelated healthy individuals. Further, protein homology modeling revealed that the change p.M186V might destabilize the interaction between the FERM-M and FERM-C domains. The in silico prediction supports pathogenicity of the mutation; nevertheless it needs in vivo validation in the future. This is the first genetic investigation of XLICN in a North Indian family where we report a novel causal mutation c.556A>G (p.M186V) in the gene FRMD7.

MTHFR C677T predisposes to POAG but not to PACG in a North Indian population: a case control study.

Hyperhomocysteinemia induced by the C677T genetic variant in MTHFR (methylenetetrahydrofolate reductase) has been implicated in neuronal cell death of retinal ganglion cells (RGC), which is a characteristic feature of glaucoma. However, association of MTHFR C677T with glaucoma has been controversial because of inconsistent results across association studies. Association between MTHFR C677T and glaucoma has not been reported in Indian population. Therefore, with a focus on neurodegenerative death of RGC in glaucoma, the current study aimed to investigate association of MTHFR C677T with Primary Open Angle Glaucoma (POAG) and Primary Angle Closure Glaucoma (PACG) in a North Indian population. A total of 404 participants (231 patients and 173 controls) were included in this study. Genotyping was performed by Polymerase Chain Reaction-Restriction Fragment Length Polymorphism. A few random samples were also tested by direct sequencing. Genotypic and allelic distributions of the POAG and PACG cohorts were compared to that of controls by chi-square test and odds ratios were reported with 95% confidence intervals. Genotypic and allelic distributions between POAG cases and controls were significantly different (p = 0.03 and p = 0.01 respectively). Unlike POAG, we did not find significant difference in the genotypic and allelic distributions of C677T between PACG cases and controls (p>0.05). We also observed a higher proportion of TT associated POAG in females than that in males. However, this is a preliminary indication of gender specific risk of C677T that needs to be replicated in a larger cohort of males and females. The present investigation on MTHFR C677T and glaucoma reveals that the TT genotype and T allele of this polymorphism are significant risk factors for POAG but not for PACG in North Indian population. Ours is the first report demonstrating association of MTHFR C677T with POAG but not PACG in individuals from North India.