Mutation in ADAMTS10 in a Canine Model of Primary Open Angle Glaucoma

Abstract

Purpose: : To identify the disease gene in a colony of Beagles with autosomal recessive primary open angle glaucoma (POAG) established as a model for human POAG.

Methods: : Dogs from the POAG Beagle colony were genotyped using the Affymetrix canine genome-wide SNP array. SNP data were analyzed by zygosity analysis (identification of SNPs that are both homozygous for all affected and heterozygous for all carriers) and genome-wide two-point linkage analysis followed by multipoint linkage analysis of regions of interest. The identified disease locus was captured and then sequenced with the Illumina Genome Analyzer II. Candidate gene expression was investigated by Western blotting of protein extracts from normal dog eye tissue. Structural homology modeling and measurement of protein half-life was performed to determine functional effects of the identified candidate variant.

Results: : A single 4 Mb locus on canine chromosome 20 (Chr20) was identified by zygosity analysis and confirmed by linkage analysis. The canine Chr20 locus is syntenic to a previously mapped locus for intraocular pressure (IOP) on human Chr19. Sequence capture and Illumina sequencing of the entire canine Chr20 locus revealed a total of 2,692 SNPs segregating with disease, 72% of which were novel. Of the disease-segregating SNPs, 52 were within exons and 8 were nonsynonomous. The strongest candidate variant causes a glycine to arginine substitution in a highly conserved region of the metalloproteinase ADAMTS10. Western blotting showed high expression of ADAMTS10 in the trabecular meshwork (TM). Homology modeling of ADAMTS10 structure revealed that the arginine substitution likely disrupts protein folding. Compared to the normal form, mutated ADAMTS10 was found to have a shorter protein half-life.

Conclusions: : Synteny of the canine POAG locus with the human Chr19 locus for IOP is consistent with the initial manifestations of disease in the POAG Beagles which is increased IOP. The function and expression pattern of ADAMTS10 is consistent with many studies implicating altered extracellular matrix in the TM in elevation of IOP. ADAMTS10 may play a role in the structure and/or function of microfibrils, suggesting that altered processing of extracellular matrix and/or defects in microfibril structure or function may be involved in raising intraocular pressure.

Keywords: gene mapping • genetics • intraocular pressure