Dataset Information

A locus for posterior polymorphous corneal dystrophy (PPCD3) maps to chromosome 10.

ABSTRACT: Posterior polymorphous corneal dystrophy (PPCD) is an autosomal dominant disorder characterized by corneal endothelial abnormalities, which can lead to blindness due to loss of corneal transparency and sometimes glaucoma. We mapped a new locus responsible for PPCD in a family in which we excluded the previously reported PPCD locus on 20q11, and the region containing COL8A2 on chromosome 1. Results of a 317-marker genome scan provided significant evidence of linkage of PPCD to markers on chromosome 10, with single-point LOD scores of 2.63, 1.63, and 3.19 for markers D10S208 (at (circumflex)theta = 0.03), D10S1780 (at (circumflex)theta = 0.00), and D10S578 (at (circumflex)theta = 0.06). A maximum multi-point LOD score of 4.35 was found at marker D10S1780. Affected family members shared a haplotype in an 8.55 cM critical interval that was bounded by markers D10S213 and D10S578. Our finding of another PPCD locus, PPCD3, on chromosome 10 indicates that PPCD is genetically heterogeneous. Guttae, a common corneal finding sometimes observed along with PPCD, were found among both affected and unaffected members of the proband's sib ship, but were absent in the younger generations of the family. Evaluation of phenotypic differences between family members sharing the same affected haplotype raises questions about whether differences in disease severity, including differences in response to surgical interventions, could be due to genetic background or other factors independent of the PPCD3 locus.

SUBMITTER: Shimizu S

PROVIDER: S-EPMC1249494 | biostudies-literature | 2004 Nov

REPOSITORIES: biostudies-literature

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A locus for posterior polymorphous corneal dystrophy (PPCD3) maps to chromosome 10.

Shimizu Satoko S Krafchak Charles C Fuse Nobuo N Epstein Michael P MP Schteingart Miriam T MT Sugar Alan A Eibschitz-Tsimhoni Maya M Downs Catherine A CA Rozsa Frank F Trager Edward H EH Reed David M DM Boehnke Michael M Moroi Sayoko E SE Richards Julia E JE

American journal of medical genetics. Part A 20041101 4

Posterior polymorphous corneal dystrophy (PPCD) is an autosomal dominant disorder characterized by corneal endothelial abnormalities, which can lead to blindness due to loss of corneal transparency and sometimes glaucoma. We mapped a new locus responsible for PPCD in a family in which we excluded the previously reported PPCD locus on 20q11, and the region containing COL8A2 on chromosome 1. Results of a 317-marker genome scan provided significant evidence of linkage of PPCD to markers on chromoso ...[more]

PMID: 15384081

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Project description:PurposeTo identify the genetic basis of posterior polymorphous corneal dystrophy 1 (PPCD1) using next-generation sequencing (NGS) of the common PPCD1 support interval, in which Sanger sequencing failed to identify a pathogenic mutation.MethodsEnrichment of the portion of chromosome 20 containing the common PPCD1 interval was performed on DNA extracted from an affected and an unaffected member of a family previously linked to the PPCD1 locus. NGS using the Roche 454 Titanium platform was performed, followed by computational analysis using NextGENe Software.ResultsNGS of the selectively enriched chromosomal 20 region between markers D20S48 and D20S190 produced over 400,000 DNA sequence reads with an average of 350 bases for each of the two DNA samples. Alignment of the DNA sequence reads with the reference sequence from the National Center of Biotechnology Information (NCBI) resulted in over 119 million matched bases per sample. Approximately 68,000 DNA sequence variants were identified in the common PPCD1 support interval in the affected individual, which was approximately twice the number of sequence variants identified in the unaffected individual. In both individuals, approximately 0.5% of the identified variants mapped to the 13 known and 16 predicted genes in the PPCD1 support interval, including 16 of the 17 (94%) variants previously identified by Sanger sequencing in the 13 known genes. In both individuals, the variant not identified by NGS was located in a region of inadequate coverage.ConclusionsNGS identified all of the exonic sequence variants that were previously identified by Sanger sequencing in known genes in adequately covered regions of the common PPCD1 interval, although the pathogenic variant is yet to be discovered. Given adequate coverage of a selectively enriched chromosomal region of interest, NGS represents a useful technique to screen for sequence variants in candidate gene loci that has multiple advantages over previously employed techniques for mutation discovery.

Project description:PURPOSE: Posterior polymorphous corneal dystrophy (PPCD) is a genetically heterogeneous autosomal dominant condition which maps to the pericentromeric region of chromosome 20. Mutations in the VSX1 transcription factor have been reported in patients affected with PPCD, keratoconus, or a combination of both phenotypes. However, no mutation was identified in the coding region of VSX1 in the family used for the original mapping. To clarify the genetic basis of PPCD1, a thorough analysis was performed on the original PPCD1 family and two other PPCD1-linked families. As part of the analysis, the expression profile, transcript variants, and evolutionary conserved regions of VSX1, a key candidate gene within the linkage interval, were characterized. METHODS: Haplotype analysis was performed using highly informative markers on the pericentromeric region of chromosome 20. VSX1 transcript variants were identified using RT-PCR and characterized by 3'RACE assay. Temporal expression profile of VSX1 was evaluated using semi-quantitative real-time RT-PCR on human tissues. Evolutionary conserved regions (ECRs) were identified in the vicinity of VSX1 using publicly available sequence alignments (UCSC and rVista) and sequenced for mutation analysis. RESULTS: Recombination events were identified that narrow the PPCD1-disease interval from 20 to 16.44 cM. This smaller interval includes the CHED1 locus and a recently described PPCD locus in Czech families. The three strongest candidate genes of the PPCD1-CHED1 overlap region (RBBP9, ZNF133, SLC24A3) did not show any mutations in our PPCD1-linked families. Semi-quantitative real-time RT-PCR detected VSX1 expression in neonatal human cornea. Six transcript variants of VSX1 were characterized. Four of the transcript variants spliced to two novel exons downstream of the gene. Mutation analysis of the PPCD1-linked families did not reveal any mutations in the full genomic sequence of VSX1 (considering all splice variants) or in the six cis- regulatory modules predicted in the vicinity of VSX1 (100 kb). CONCLUSIONS: This is the first documentation of VSX1 expression in human neonatal cornea. We provide evidence for genetic heterogeneity of chromosome 20-related PPCD and refinement of the original PPCD1 interval. The full genomic sequence of VSX1 and coding exons of three other candidate genes were excluded from being pathogenic in the original PPCD1 family.

Project description:ImportanceThe identification of steep corneal curvatures in a significant percentage of patients with posterior polymorphous corneal dystrophy (PPCD) confirms this previously reported association and suggests a role for the ZEB1 protein in keratocyte function.ObjectiveTo determine whether PPCD is characterized by significant corneal steepening.Design, setting, and participantsCross-sectional study at university-based and private ophthalmology practices of 38 individuals (27 affected and 11 unaffected) from 23 families with PPCD.ExposureSlitlamp examination and corneal topographic imaging were performed for individuals with PPCD and unaffected family members. Saliva or blood samples were obtained from each individual for DNA isolation and ZEB1 sequencing. Corneal ZEB1 expression was measured using immunohistochemistry.Main outcomes and measuresPercentage of individuals affected with PPCD and controls with an average keratometric value greater than 48.0 diopters (D) in each eye; the mean keratometric value averaged for both eyes of individuals with PPCD and controls; and the correlation of ZEB1 mutation with keratometric value.ResultsZEB1 coding region mutations were identified in 7 of the 27 affected individuals. Ten of the 38 individuals (26.3%) had average keratometric values greater than 48.0 D OU: 10 of 27 individuals with PPCD (37.0%; 6 of 7 individuals with ZEB1 mutations [85.7%] and 4 of 20 individuals without ZEB1 mutations [20.0%]) and 0 of 11 unaffected individuals (P = .04 for unaffected vs affected individuals; P = .004 for individuals with PPCD with vs without ZEB1 mutation). The mean keratometric value of each eye of affected individuals (48.2 D) was significantly greater than that of each eye of unaffected family members (44.1 D) (P = .03). Affected individuals with ZEB1 mutations demonstrated a mean keratometric value of 53.3 D, which was significantly greater than that of affected individuals without ZEB1 mutations (46.5 D; P = .004). Fluorescence immunohistochemistry demonstrated ZEB1 expression in keratocyte nuclei.Conclusions and relevanceAbnormally steep corneal curvatures are identified in 37% of all individuals with PPCD and 86% of affected individuals with PPCD secondary to ZEB1 mutations. ZEB1 is present in keratocyte nuclei, suggesting a role for ZEB1 in keratocyte function. Therefore, ZEB1 may play a role in both corneal stromal and endothelial development and function, and PPCD should be considered both an endothelial dystrophy and an ectatic disorder.

Dataset Information

A locus for posterior polymorphous corneal dystrophy (PPCD3) maps to chromosome 10.

Publications

A locus for posterior polymorphous corneal dystrophy (PPCD3) maps to chromosome 10.

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