title: Mitochondrial DNA nucleotide changes in primary congenital glaucoma patients.
abstract: OBJECTIVE
  Primary congenital glaucoma (PCG) is the second most common cause of blindness, accounting for 0.01%-0.04% of total blindness worldwide. Most congenital glaucoma cases are mapped to the GLC3A locus, and many aspects of PCG are still unknown. Recent studies have reported an increased frequency of mitochondrial DNA (mtDNA) sequence changes in primary open-angle glaucoma, primary angle-closure glaucoma, and pseudoexfoliation glaucoma compared to controls. Thus, this study was planned with the aim of detecting mitochondrial DNA variations in PCG cases.
  
  
  METHODS
  Twenty primary congenital glaucoma cases were selected from Dr. R. P. Centre for Ophthalmic Sciences of All India Institute of Medical Sciences (AIIMS), New Delhi, India. DNA was isolated from whole blood samples. The entire coding region of the mitochondrial genome was amplified by PCR in 20 patients and 20 controls. The full mtDNA genome was sequenced and analyzed against mitochondrial reference sequence NC_012920.
  
  
  RESULTS
  MtDNA sequencing revealed a total of 195 nucleotide variations in PCG patients and 58 in controls. Of the 195 changes, 43 (22.05%) were nonsynonymous, 82 (42.05%) were synonymous, and 30 were in RNA genes. A total of 39/195 (20.00%) variations were observed in the D-loop (hypervariable region), 19/195 (9.74%) in different ribosomal RNA (rRNAs), 11/195 (5.64%) in transfer RNA (tRNAs), 66/195 (33.84%) in complex I, 17/195 (8.71%) in complex III, 27/195 (13.84%) in complex IV, and 15/195 (7.69%) in complex V. Of 58 variations in the controls, 14 were nonsynonymous changes. The Sorting Intolerant from Tolerant and Polymorphism Phenotyping analyses of all nonsynonymous changes from patients revealed two pathogenic changes in NADH-ubiquinone oxidoreductase chain 2 (ND2) and cytochrome oxidase subunit III (COXIII) subunits. In one of the patients, the insertion of cytosine introduced a frame shift change (p.Ile104AsnfsX26) in the cytochrome b (CYB) subunit of the electron transport chain. In another patient, a variation (G8572A) in ATP synthase 8 (ATpase8) led to the introduction of a stop codon or termination at amino acid position 69. Haplogroup/phylogenetic analysis of mtDNA showed that primary congenital glaucoma patients belong to three macrohaplogroups: M (4), N (15), and L (1). Fifty percent of the patients belonged to the H2a2a lineage of the N-derived haplogroup.
  
  
  CONCLUSIONS
  Although several mutations were found at a higher frequency among our population, there is a need to complement this study with functional studies and to analyze a large number of samples in different populations of different haplogroups, as penetrance varies among haplogroups.
authors: Laboratory for Molecular Reproduction and Genetics, Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India.
authors: Manoj
authors: M
authors: Kumar
authors: Mukesh
authors: M
authors: Tanwar
authors: Muneeb Ahmad
authors: MA
authors: Faiq
authors: Jhumur
authors: J
authors: Pani
authors: Monis Bilal
authors: MB
authors: Shamsi
authors: Tanuj
authors: T
authors: Dada
authors: Rima
authors: R
authors: Dada
mesh_terms: D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D045303:Cytochromes b / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000235:genetics; D005260:Female; D014644:Genetic Variation; D054629:Genome, Mitochondrial; D005901:Glaucoma / Q000151:congenital* / Q000235:genetics*; D006239:Haplotypes; D006801:Humans; D007223:Infant; D008297:Male; D025261:Mitochondrial Proton-Translocating ATPases / Q000235:genetics; D009154:Mutation; D009245:NADH Dehydrogenase / Q000235:genetics
chemical_list: D004272:DNA, Mitochondrial; D045303:Cytochromes b; D009245:NADH Dehydrogenase; C521326:NADH dehydrogenase subunit 2, human; D003576:Electron Transport Complex IV; C513300:MT-ATP8 protein, human; D025261:Mitochondrial Proton-Translocating ATPases
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