title: An unusual presentation of macular corneal dystrophy associated with uniparental isodisomy and a novel Leu173Pro mutation.
abstract: OBJECTIVE
  To report an unusual phenotype of macular corneal dystrophy (MCDC1) associated with a novel CHST6 mutation transmitted via maternal isodisomy.
  
  
  METHODS
  Slit lamp examination of the patient and his parents was performed. DNA was collected from each individual for amplification and sequencing of the CHST6 coding region, as well as exons 4 and 12 of TGFBI. Serum antigenic keratan sulfate (AgKS) levels were measured for confirmation of the diagnosis and subtyping of MCDC1. Quantitative real-time PCR (qPCR) was performed to differentiate between homozygous and hemizygous sequence variants. Genotyping at 12 single nucleotide polymorphisms (SNPs) within and surrounding CHST6 was performed to determine the pattern of inheritance of mutations identified in CHST6.
  
  
  RESULTS
  Examination of the proband revealed bilateral, discrete, axially distributed, gray-white deposits at the level of Bowman's layer, with diffuse fine corneal stromal haze. Screening of TGFBI exons 4 and 12 in the proband did not reveal any allelic variants. However, screening of CHST6 in the proband demonstrated a novel homozygous missense mutation involving a highly conserved amino acid (c.518T > C; Leu173Pro) and undetectable serum AgKS levels in the proband confirmed the diagnosis of type I MCDC1. Quantitative PCR confirmed that both copies of CHST6 were present in the patient, excluding the possibility that the mutation was present in the hemizygous state. The results of genotyping were consistent with maternal isodisomy, as the patient was homozygous for an allele possessed by his mother at each SNP, two of which were informative and demonstrated nonpaternal inheritance.
  
  
  CONCLUSIONS
  A phenotypically unusual variant of MCDC1 was found to be associated with the novel Leu173Pro mutation in CHST6, transmitted via uniparental isodisomy, a previously unreported pattern of inheritance in the corneal dystrophies.
authors: Cornea Service, Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, California 90095, USA.
authors: Vivek S
authors: VS
authors: Yellore
authors: Baris
authors: B
authors: Sonmez
authors: Michael C
authors: MC
authors: Chen
authors: Sylvia A
authors: SA
authors: Rayner
authors: Eugene J
authors: EJ
authors: Thonar
authors: Anthony J
authors: AJ
authors: Aldave
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D017124:Conserved Sequence; D003315:Cornea / Q000473:pathology; D003317:Corneal Dystrophies, Hereditary / Q000097:blood / Q000235:genetics* / Q000473:pathology*; D005838:Genotype; D006720:Homozygote; D006801:Humans; D007632:Keratan Sulfate / Q000097:blood; D007930:Leucine; D008297:Male; D009154:Mutation; D020125:Mutation, Missense; D010375:Pedigree; D016133:Polymerase Chain Reaction / Q000379:methods; D020641:Polymorphism, Single Nucleotide; D011392:Proline; D015238:Sulfotransferases / Q000235:genetics*; D024182:Uniparental Disomy; D000097811:Carbohydrate Sulfotransferases
chemical_list: D007632:Keratan Sulfate; D007930:Leucine; D011392:Proline; D015238:Sulfotransferases; D000097811:Carbohydrate Sulfotransferases