A novel missense mutation in ADAMTS10 in Norwegian Elkhound primary glaucoma

Abstract

Primary glaucoma is one of the most common causes of irreversible blindness both in humans and in dogs. Glaucoma is an optic neuropathy affecting the retinal ganglion cells and optic nerve, and elevated intraocular pressure is commonly associated with the disease. Glaucoma is broadly classified into primary open angle (POAG), primary closed angle (PCAG) and primary congenital glaucoma (PCG). Human glaucomas are genetically heterogeneous and multiple loci have been identified. Glaucoma affects several dog breeds but only three loci and one gene have been implicated so far. We have investigated the genetics of primary glaucoma in the Norwegian Elkhound (NE). We established a small pedigree around the affected NEs collected from Finland, US and UK and performed a genome-wide association study with 9 cases and 8 controls to map the glaucoma gene to 750 kb region on canine chromosome 20 (praw = 4.93×10-6, pgenome = 0.025). The associated region contains a previously identified glaucoma gene, ADAMTS10, which was subjected to mutation screening in the coding regions. A fully segregating missense mutation (p.A387T) in exon 9 was found in 14 cases and 572 unaffected NEs (pFisher = 3.5×10-27) with a high carrier frequency (25.3%). The mutation interrupts a highly conserved residue in the metalloprotease domain of ADAMTS10, likely affecting its functional capacity. Our study identifies the genetic cause of primary glaucoma in NEs and enables the development of a genetic test for breeding purposes. This study establishes also a new spontaneous canine model for glaucoma research to study the ADAMTS10 biology in optical neuropathy.

Figure 1. Pedigree of glaucoma affected Norwegian Elkhounds.

The pedigree constructed around affected dogs indicates a likely recessive mode of inheritance as the affected dogs are born to unaffected parents and there are multiple affected littermates in some litter. The squared dogs were included in the GWAS. Individuals marked with yellow background were genotyped as obligatory carriers and were all heterozygous for the mutation.

Figure 2. Genome wide association study.

A) A Manhattan plot of genome-wide case-control association analysis with 8 cases and 9 controls indicate the most highly associated region in CFA20. B) The glaucoma associated region on chromosome 20 spans from 53.1 Mb to 53.8 Mb. C) Genotypes at the associated region on CFA20. All cases share a 750 kb homozygous block. D) The associated region harbors 35 genes of which only ADAMTS10 has been associated with POAG.

Figure 3. A missense mutation in the ADAMTS10.

A) A schematic representation of the ADAMTS10 gene structure. The gene is composed of 24 coding exons (dark blue) and the c.1441G>A variant is positioned in the exon 9 (not in scale). B) Chromatograms of the non-synonymous variant position in an affected, a carrier and a wild-type dog. C) The p.A387T variant is positioned in the catalytic metalloprotease domain.