Screening ADAMTS10 in dog populations supports Gly661Arg as the glaucoma-causing variant in beagles

Abstract

Purpose: Previously, we mapped the disease locus in the beagle model of autosomal recessive primary open angle glaucoma (POAG) to a 4-Mb interval on chromosome 20, and identified a Gly661Arg variant in ADAMTS10 as the candidate disease-causing variant. The purpose of this study was to test the hypothesis that the Gly661Arg variant of ADAMTS10 causes glaucoma by genotyping dogs of various breeds affected and unaffected by primary glaucoma.

Methods: Dogs of various breeds, affected or unaffected with primary glaucoma, were genotyped for the Gly661Arg variant of ADAMTS10, as well as 7 other nonsynonymous single nucleotide polymorphisms (SNPs) in other genes in the beagle POAG locus that segregate with disease. Alternate allele frequencies were calculated with 95% confidence intervals and comparisons made to expected allele frequency relative to disease prevalence or between cases and controls.

Results: For the nonsynonymous SNPs other than the ADAMTS10 variant, control dogs were identified that were homozygous for the alternative alleles, ruling out those variants as causative. None of the nonsynonymous SNPs were found associated with primary glaucoma in American cocker spaniels. The Gly661Arg variant of ADAMTS10 was the only variant with minor allele frequency consistent with the prevalence of primary glaucoma in the general beagle population. The only dog found homozygous for the Gly661Arg variant of ADAMTS10 was an affected beagle, unrelated to the POAG colony.

Conclusions: These findings support the Gly661Arg mutation of ADAMTS10 as the likely cause of POAG in beagles.

Figure 1

Nonsynonymous SNPs segregating with disease in the beagle glaucoma colony. The locations of the eight nonsynonymous SNPs that segregate with disease in the POAG beagle colony are indicated by arrows labeled according to the gene in which the SNPs are located. The nonsynonymous SNPs are clustered in a region of approximately 1.2 Mb within the 4-Mb beagle glaucoma locus, represented by the gray bar, below which the location on canine chromosome 20 is indicated, based on the CanFam 2 reference canine genome. Two SNPs were found in GPCR108.

Figure 2

Beagles genotyped for the nonsynonymous SNPs in the beagle glaucoma locus. Beagles not affected by glaucoma from two different animal supplier colonies (A, B) and from veterinary clinics (C) were genotyped for the eight nonsynonymous SNPs in the beagle glaucoma locus that segregated with disease in the beagle glaucoma colony. The key for genotype calls is shown (A). Each horizontal row represents the haplotype of one or more dogs, with number of dogs represented to the left of the row (A–C). The gene containing each variant is indicated above (A). In GPCR108, there are two nonsynonymous SNPs, GPCR108 (1) and GPCR108 (2). Minor allele frequencies for the variants are shown for the supplier colonies and clinic samples (D) with error bars representing +/− 95% CIs. The alternative allele frequency upper threshold of 10% for a putative disease allele in beagles is indicated by the dashed line (D).

Figure 3

Control dogs of various breeds genotyped for the nonsynonymous SNPs in the beagle glaucoma locus. Dogs of various breeds, not affected by glaucoma, were genotyped for the eight nonsynonymous SNPs that segregated with disease in the beagle glaucoma colony. Each horizontal row represents the haplotype of an individual dog. The gene containing each variant is indicated above. Genotypes are displayed as in Figure 2.

Figure 4

American cocker spaniels affected and unaffected by primary glaucoma genotyped for the nonsynonymous SNPs in the beagle glaucoma locus. Minor allele frequencies for the variants are shown for 26 unaffected (open symbols) and 16 affected (closed symbols) American cocker spaniels. Error bars represent +/− 95% CIs.

Figure 5

Affected dogs of various breeds genotyped for the nonsynonymous SNPs in the beagle glaucoma locus. Bassett Hounds (A), dogs of various breeds (B), and a beagle (C), affected by primary glaucoma, were genotyped for the eight nonsynonymous SNPs in the beagle glaucoma locus. Each horizontal row represents the haplotype of an individual dog. The gene containing each variant is indicated above. Genotypes are displayed as in Figure 2.