Macular corneal dystrophy type I and type II are caused by distinct mutations in a new sulphotransferase gene.

Macular corneal dystrophy (MCD; MIM 217800) is an autosomal recessive hereditary disease in which progressive punctate opacities in the cornea result in bilateral loss of vision, eventually necessitating corneal transplantation. MCD is classified into two subtypes, type I and type II, defined by the respective absence and presence of sulphated keratan sulphate in the patient serum, although both types have clinically indistinguishable phenotypes. The gene responsible for MCD type I has been mapped to chromosome 16q22, and that responsible for MCD type II may involve the same locus. Here we identify a new carbohydrate sulphotransferase gene (CHST6), encoding an enzyme designated corneal N-acetylglucosamine-6-sulphotransferase (C-GlcNAc6ST), within the critical region of MCD type I. In MCD type I, we identified several mutations that may lead to inactivation of C-GlcNAc6ST within the coding region of CHST6. In MCD type II, we found large deletions and/or replacements caused by homologous recombination in the upstream region of CHST6. In situ hybridization analysis did not detect CHST6 transcripts in corneal epithelium in an MCD type II patient, suggesting that the mutations found in type II lead to loss of cornea-specific expression of CHST6.

Akama TO ，Nishida K ，Nakayama J ，Watanabe H ，Ozaki K ，Nakamura T ，Dota A ，Kawasaki S ，Inoue Y ，Maeda N ，Yamamoto S ，Fujiwara T ，Thonar EJ ，Shimomura Y ，Kinoshita S ，Tanigami A ，Fukuda MN ... -  《NATURE GENETICS》

Identification of novel mutations in the carbohydrate sulfotransferase gene (CHST6) causing macular corneal dystrophy.

Macular corneal dystrophy (MCD) is a rare corneal dystrophy that is characterized by abnormal deposits in the corneal stroma, keratocytes, Descemet's membrane, and endothelium, accompanied by progressive clouding. It has been classified into three immunophenotypes--MCD types I, IA, and II--according to the serum level of sulfated keratan sulfate (KS) and immunoreactivity of the corneal tissue. Recently, mutations in a new carbohydrate sulfotransferase gene (CHST6) encoding corneal glucosamine N-acetyl-6-sulfotransferase (C-GlcNac-6-ST) have been identified as the cause of MCD. Mutation screening of the CHST6 gene has been undertaken to identify the underlying mutations in five unrelated British families with MCD. DNA was extracted from venous blood obtained from all participants, and the coding region of CHST6 was amplified by polymerase chain reaction (PCR). The PCR products were analyzed by direct sequencing and restriction enzyme digestion. Enzyme-linked immunosorbent assay (ELISA) was performed to assess the presence of KS in serum from the probands of MCD-affected families participating in the study. Six novel missense mutations--four homozygous and two compound heterozygous--were identified in the CHST6 gene. The ELISA showed that the disease in all patients participating in the study was of MCD type I, including the subtype IA. These novel mutations are thought to result in loss of corneal sulfotransferase function, which would account for the MCD phenotype.

El-Ashry MF ，Abd El-Aziz MM ，Wilkins S ，Cheetham ME ，Wilkie SE ，Hardcastle AJ ，Halford S ，Bayoumi AY ，Ficker LA ，Tuft S ，Bhattacharya SS ，Ebenezer ND ... -  《INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE》

Macular corneal dystrophy types I and II are caused by distinct mutations in the CHST6 gene in Iceland.

To identify CHST6 mutations in five additional Icelandic cases of macular corneal dystrophy (MCD) type I and in four families with MCD type II from Iceland. Genomic DNA was extracted from blood leukocytes of patients with MCD, their healthy family members, and from control individuals. CHST6 mutations were determined by PCR-sequencing. Immunophenotypes of MCD were determined by measuring antigenic keratan sulfate (AgKS) levels in serum and by an immunohistochemical study on corneal tissue. Five additional cases of MCD type I and four families with MCD type II from Iceland were studied. A homozygous p.A128V mutation in the coding region of the CHST6 gene was identified in four of the five MCD type I cases. The other person with MCD type I was a compound heterozygote for p.A128V and a frameshift p.V6fs resulting from a 10-base pair insertion (c.15_16insATGCTGTGCG). Four of five individuals with MCD type II were compound heterozygotes for p.A128V and p.V329L, thus sharing the same p.A128V mutation as MCD type I. One patient with MCD type II was homozygous for p.V329L. The p.V329L mutation was only found in MCD type II patients. An analysis of the upstream region of CHST6 disclosed no upstream deletion or replacements in Icelandic patients with MCD type II. The findings fit the haplotype analysis that we reported previously in Icelandic MCD families and indicate that different mutations in CHST6 cause MCD type I and type II in Iceland.

Liu NP ，Smith CF ，Bowling BL ，Jonasson F ，Klintworth GK ... -  《MOLECULAR VISION》

Mutations in corneal carbohydrate sulfotransferase 6 gene (CHST6) cause macular corneal dystrophy in Iceland.

Macular corneal dystrophy (MCD) is subdivided into three immunophenotypes (MCD types I, IA and II). Recently, mutations in the carbohydrate sulfotransferase 6 gene (CHST6) were identified to cause MCD. The purpose of this study was to examine CHST6 for mutations in Icelandic patients with MCD type I. Genomic DNA was extracted from leukocytes in the peripheral blood and the coding region of CHST6 was examined for mutations by polymerase chain reaction (PCR) and direct sequencing. Mutation analysis of the CHST6 coding region identified three different mutations in sixteen Icelandic patients with MCD type I. Eleven patients with MCD type I were homozygous for a C1075T mutation. One patient with MCD type I was found to be a compound heterozygous for C1075T and G1189C mutations. One family with MCD type I contained a 10 base pair insertion (ATGCTGTGCG) between nucleotides 707 and 708. In this family, two affected siblings had a homozygous insertion while both their affected mother and their affected maternal aunt had a heterozygous insertion and a heterozygous C1075T mutation. Three different nucleotide changes were identified in the coding region of CHST6 in sixteen Icelandic patients with MCD type I. All three of these alterations are predicted to affect the translated protein and each of them corresponded to a particular disease haplotype that we had previously reported in this population.

Liu NP ，Dew-Knight S ，Rayner M ，Jonasson F ，Akama TO ，Fukuda MN ，Bao W ，Gilbert JR ，Vance JM ，Klintworth GK ... -  《MOLECULAR VISION》

Different mutations in carbohydrate sulfotransferase 6 (CHST6) gene cause macular corneal dystrophy types I and II in a single sibship.

The aim of this study was to examine the carbohydrate sulfotransferase 6 (CHST6) gene for mutations in a sibship with both macular corneal dystrophy (MCD) types I and II. Clinically relevant laboratory investigation. The coding region of the CHST6 gene was examined for mutations. In one sibling, MCD type I was due to a homozygous C1110T (Arg140end) mutation in CHST6. Two MCD type II individuals exhibited three heterozygous nucleotide changes: C1110T, G1360A (Gly223Asp), and G1685T (Gln331His). Analysis of the upstream region was performed on one individual with MCD type II, and no upstream deletion or substitution was found. These findings fit the haplotype analysis that we reported previously and indicate that the predicted protein that is encoded by CHST6 is more severely affected in the individual with MCD type I than in the siblings with MCD type II.

Liu NP ，Bao W ，Smith CF ，Vance JM ，Klintworth GK ... -  《AMERICAN JOURNAL OF OPHTHALMOLOGY》