Exclusion of positional candidate gene coding region mutations in the common posterior polymorphous corneal dystrophy 1 candidate gene interval.
OBJECTIVE
Posterior polymorphous corneal dystrophy (PPCD) is an autosomal-dominant disorder of the corneal endothelium associated with visually significant corneal edema and glaucoma. Statistical genetic analysis of 4 families with PPCD has demonstrated linkage to a 2.4 cM common support interval on chromosome 20 bordered by the markers D20S182 and D20S139. We sought to identify the genetic basis of PPCD linked to chromosome 20 (PPCD1) by screening the 26 positional candidate genes between these markers in a family previously mapped to the PPCD1 region.


METHODS
The coding regions of the 26 positional candidate genes mapped to the common PPCD1 support interval were amplified and sequenced in affected and unaffected individuals from a family previously linked to the PPCD1 locus. Nine other genes positioned just outside of the common PPCD1 support interval but within the autosomal-dominant congenital hereditary endothelial dystrophy interval were also screened.


RESULTS
Four DNA sequence variants in 3 of the positional candidate genes demonstrated complete segregation with the affected phenotype: p.Thr109Thr (rs6111803) in OVOL2, p.Arg56Gln (novel variant-RPSnovel) in RPS19P1, and p.Thr85Thr (rs1053834) and p.Pro99Ser (rs1053839) in C20orf79. Each of these 4 sequence variants demonstrated significant linkage with the affected phenotype in this family (P = 2.5 x 10 for RPSnovel, rs1053834 and rs1053839; P = 8.6 x 10 for rs6111803). However, we also identified each of these 4 sequence variants in > or = affected control individuals. The haplotype on which the disease-causing mutation is segregating was found to have a population frequency of 4.2% in the CEPH HapMap trios. Although a number of other previously described and novel single nucleotide polymorphisms were identified in the 35 positional candidate genes located within the PPCD1 and congenital hereditary endothelial dystrophy intervals, none segregated with the affected phenotype.


CONCLUSIONS
We report the absence of a presumed pathogenic coding region mutation in the common PPCD1 support interval. Although minor alleles of 4 single nucleotide polymorphisms were identified that segregated with the affected phenotype, the relatively high frequency of each minor allele in the general population indicates that none is a candidate for the causal variant for PPCD. Instead, the causal variant is most likely a coding region deletion or a variant in a noncoding region of the PPCD1 common support interval.
Aldave
Anthony J
AJ
The Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA. aldave@jsei.ucla.edu
Yellore
Vivek S
VS
Vo
Rosalind C
RC
Kamal
Khairidzan M
KM
Rayner
Sylvia A
SA
Plaisier
Christopher L
CL
Chen
Michael C
MC
Damani
Mausam R
MR
Pham
Michele N
MN
Gorin
Michael B
MB
Sobel
Eric
E
Papp
Jeanette
J
D002890:Chromosomes, Human, Pair 20 / Q000235:genetics*; D003317:Corneal Dystrophies, Hereditary / Q000235:genetics*; D015715:Corneal Edema / Q000151:congenital; D004728:Endothelium, Corneal / Q000473:pathology; D005260:Female; D005784:Gene Amplification; D008040:Genetic Linkage; D005901:Glaucoma / Q000151:congenital; D006801:Humans; D008297:Male; D009154:Mutation; D016366:Open Reading Frames / Q000235:genetics*; D010375:Pedigree; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011506:Proteins / Q000235:genetics*; D014157:Transcription Factors
C544941:Ovol2 protein, human; D011506:Proteins; D014157:Transcription Factors