Prevalence of primary mutations in Leber hereditary optic neuropathy: A five-year report from a tertiary eye care center in India.

PURPOSE: Genetic testing for primary mutations m.3460G>A, m.11778G>A, and m.14484T>C in ND1, ND4, and ND6 genes of mitochondrial DNA is the recommended assay for Leber hereditary optic neuropathy (LHON; OMIM 535000). This report discusses the outcome of molecular genetic screening for these three primary mutations in suspected LHON cases in India. METHODS: Two hundred and seventy-eight unrelated presumed LHON patients who were seen at the neuro-ophthalmology clinic of a tertiary eye care center from 2014-2018 were analyzed. They were genotyped for the three common variants by polymerase chain reaction-based direct sequencing, and their plasmy status was also determined by restriction enzyme digestion. RESULTS: Eighty two of 278 patients were positive for one of the 3 common mutations with m.11778G>A in ND4 gene more frequently distributed (N=72) in homoplasmic state (N=59/82). The mean onset age of visual loss was 21.1years (SD, 9.8 years; range, 5-58 years) in patients harboring the primary mutation. The most common clinical presentation was bilateral sequential painless vision loss with central and cecocentral scotomas in the visual field due to optic disc atrophy. CONCLUSIONS: The study subjects are a sample of a much larger number of suspected LHON cases tested for primary mutations in India. (N= 278) and 29.4% (82/278) of patients harbour one of the 3 common mutations. Screening the entire mitochondrial genome and the other nuclear genes encoding mitochondrial protein, would probably aid in identifying the other less common mtDNA mutations causing LHON in Indian population.

Leber hereditary optic neuropathy-new insights and old challenges.

Leber hereditary optic neuropathy (LHON) is the most common primary mitochondrial DNA (mtDNA) disorder with the majority of patients harboring one of three primary mtDNA point mutations, namely, m.3460G>A (MTND1), m.11778G>A (MTND4), and m.14484T>C (MTND6). LHON is characterized by bilateral subacute loss of vision due to the preferential loss of retinal ganglion cells (RGCs) within the inner retina, resulting in optic nerve degeneration. This review describes the clinical features associated with mtDNA LHON mutations and recent insights gained into the disease mechanisms contributing to RGC loss in this mitochondrial disorder. Although treatment options remain limited, LHON research has now entered an active translational phase with ongoing clinical trials, including gene therapy to correct the underlying pathogenic mtDNA mutation.

Homozygosity mapping guided next generation sequencing to identify the causative genetic variation in inherited retinal degenerative diseases.

Inherited retinal degeneration (IRD) are a group of genetically heterogeneous disease of which retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) are the most common and severe type. In our study we had taken three unrelated South Indian consanguineous IRD families. Homozygosity mapping was done using Affymetrix 250K Nsp1 GeneChip in each of LCA, Cone-Rod dystrophy (CRD) and autosomal recessive RP (arRP) families followed by targeted re-sequencing by next generation sequencing (NGS) on Illumina MiSeq. Known candidate genes ranging from 1-8 in numbers within the homozygous blocks were identified by homozygosity mapping and targeted NGS revealed the causative mutations; RDH12 c.832A>C, ABCA4 c.1462G>T, CDHR1c.1384_1392delCTCCTGGACinsG, in the LCA, CRD and arRP families, respectively. The identified mutations were validated by Sanger sequencing, segregation in the families and their absence in 200 control chromosomes. Homozygosity mapping guided targeted NGS, especially when more numbers of known candidate genes within the homozygous blocks are observed is a comprehensive method for mutation identification. Molecular data from a larger retinal degenerative disease cohort would reveal the spectrum and prevalence of mutations and genes in Indian population. Molecular diagnosis also aids in genetic counseling, offering carrier and prenatal testing to family members.

Retinitis pigmentosa: mutation analysis of RHO, PRPF31, RP1, and IMPDH1 genes in patients from India.

PURPOSE: To screen for possible disease-causing mutations in rhodopsin (RHO), pre-mRNA processing factor 31 (PRPF31), retinitis pigmentosa 1 (RP1), and inosine monophosphate dehydrogenase 1 (IMPDH1) genes in Indian patients with isolated and autosomal dominant forms of retinitis pigmentosa (adRP). Information on such data is not available in India and hence this study was undertaken. METHODS: Blood samples were obtained from 48 isolated and 53 adRP patients, who were recruited for the study. Each patient underwent a detailed clinical examination. Genomic DNA was extracted from the blood samples and screened for mutations in four genes using an ABI3100 Avant genetic analyzer. Reverse transcriptase polymerase chain reaction was performed to amplify the mutated (IVS6+1G/A) mRNA of PRPF31 in a two-generation adRP family. RESULTS: Of the 101 probands analyzed, three harbored possible disease-causing mutations. Pathogenic changes were observed in RHO and PRPF31. A RHO mutation, p.Gly106Arg, was found in an isolated RP patient with sectoral RP. Two novel, heterozygous mutations were identified in PRPF31: p.Lys120GlufsX122 in an isolated RP patient and a splice site mutation, IVS6+1G/A in an adRP patient. However, no disease-causing changes were observed in RP1 and IMPDH1. CONCLUSIONS: We screened RHO, PRPF31, RP1, and IMPDH1 and identified causative mutations in 4% of isolated and 2% of adRP patients from India. To the best of our knowledge, this is the first report to identify frequencies of mutations in isolated and adRP patients in India.