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Genetic analysis of chromosome 20-related posterior polymorphous corneal dystrophy: genetic heterogeneity and exclusion of three candidate genes.

Hosseini SM, Herd S, Vincent AL, Héon E - Mol. Vis. (2008)

Bottom Line: The three strongest candidate genes of the PPCD1-CHED1 overlap region (RBBP9, ZNF133, SLC24A3) did not show any mutations in our PPCD1-linked families.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).This is the first documentation of VSX1 expression in human neonatal cornea.

View Article: PubMed Central - PubMed

Affiliation: Program in Genetics and Genome Biology, The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.

ABSTRACT

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.

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Ideogram of chromosome 20 showing PPCD1 minimal disease interval in different families. Bars on the left represent the disease intervals for PPCD1 and CHED1 as originally described [6,10]. Bars on the right show the refinements made in our study. Family 1 is the family used for mapping the locus (further refinement). Family 3 is the family described by Heon et al. [11] with a known VSX1 mutation. Cz1 and Cz2 represent Czech families described by Gwilliam et al. [39].
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f7: Ideogram of chromosome 20 showing PPCD1 minimal disease interval in different families. Bars on the left represent the disease intervals for PPCD1 and CHED1 as originally described [6,10]. Bars on the right show the refinements made in our study. Family 1 is the family used for mapping the locus (further refinement). Family 3 is the family described by Heon et al. [11] with a known VSX1 mutation. Cz1 and Cz2 represent Czech families described by Gwilliam et al. [39].

Mentions: There was no evidence of haplotype sharing between these families (data not shown). Figure 7 schematically summarizes the disease intervals for the PPCD1 families described to date including our recent data. These data suggest heterogeneity at PPCD1 locus by breaking it to two intervals. The disease interval for family 3, known to have a VSX1 mutation, is definitely distinct from the CHED1-PPCD1 overlap interval described in Czech families (see discussion) [39].


Genetic analysis of chromosome 20-related posterior polymorphous corneal dystrophy: genetic heterogeneity and exclusion of three candidate genes.

Hosseini SM, Herd S, Vincent AL, Héon E - Mol. Vis. (2008)

Ideogram of chromosome 20 showing PPCD1 minimal disease interval in different families. Bars on the left represent the disease intervals for PPCD1 and CHED1 as originally described [6,10]. Bars on the right show the refinements made in our study. Family 1 is the family used for mapping the locus (further refinement). Family 3 is the family described by Heon et al. [11] with a known VSX1 mutation. Cz1 and Cz2 represent Czech families described by Gwilliam et al. [39].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2267740&req=5

f7: Ideogram of chromosome 20 showing PPCD1 minimal disease interval in different families. Bars on the left represent the disease intervals for PPCD1 and CHED1 as originally described [6,10]. Bars on the right show the refinements made in our study. Family 1 is the family used for mapping the locus (further refinement). Family 3 is the family described by Heon et al. [11] with a known VSX1 mutation. Cz1 and Cz2 represent Czech families described by Gwilliam et al. [39].
Mentions: There was no evidence of haplotype sharing between these families (data not shown). Figure 7 schematically summarizes the disease intervals for the PPCD1 families described to date including our recent data. These data suggest heterogeneity at PPCD1 locus by breaking it to two intervals. The disease interval for family 3, known to have a VSX1 mutation, is definitely distinct from the CHED1-PPCD1 overlap interval described in Czech families (see discussion) [39].

Bottom Line: The three strongest candidate genes of the PPCD1-CHED1 overlap region (RBBP9, ZNF133, SLC24A3) did not show any mutations in our PPCD1-linked families.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).This is the first documentation of VSX1 expression in human neonatal cornea.

View Article: PubMed Central - PubMed

Affiliation: Program in Genetics and Genome Biology, The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.

ABSTRACT

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.

Show MeSH
Related in: MedlinePlus