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Primary Open Angle Glaucoma Beagle Type (POAG)
| Acronym: | POAG |
| Gene: | ADAMTS10 |
| Mutation: | c.1981G>A |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Primary open angle glaucoma Beagle type is an eye disorder causing a build-up of pressure in the eye. Glaucoma is divided into two categories, primary and secondary glaucoma. Primary glaucoma is characterized by its onset without any other ocular cause, while secondary glaucoma appears when another cause is present, which triggers glaucoma. Primary open angle glaucoma belongs in the group of primary glaucoma together with primary angle closure glaucoma (PACG) and primary congenital glaucoma (PCG). In Beagles, other than POAG, PACG has been identified as well. However, PACG is very rare and no research or studies have been made and no DNA tests have been made for it. Primary open angle glaucoma in Beagles has similar conditions to glaucoma in humans which is the leading cause of blindness worldwide. For this reason, POAG in Beagles is used as an animal model for human disease.
The fluid inside of the eye is called aqueous humor. It is produced behind the iris, in the ciliary body. This fluid flows through the eye and drains from the eye, maintaining normal eye pressure. The drain network in the eye is called the drainage angle or drainage canal. The inadequate outflow of aqueous humor causes a buildup of pressure, and consequently, glaucoma. Prolonged intraocular pressure results in irreversible damage to optic nerves. It can also lead to luxation of the lens and narrowing of the iridocorneal angle. On average, the intraocular pressure starts to increase at 8 to 16 months of age. The eyes of the affected dog may appear painful, pupils are red and dilated. Behavioral changes may appear as well, such as loss of appetite and eye scratching. POAG is a progressive disorder and although the symptoms occur at an early age, their early identification is rare and is not made until the late stages of the disease. Like other forms of glaucoma, POAG can be treatable, if it is detected early enough. Unfortunately, due to its progressive nature, the owners do not detect POAG until blindness onset, the final stage of POAG which is not treatable. Primary open angle glaucoma Beagle type (POAG) is caused by a point mutation in the ADAMTS10 gene. Pedigree analysis of affected dogs shows that POAG is inherited as an autosomal recessive disorder. Healthy parents of an affected dog are obligate heterozygotes and therefore carry one mutant allele. Heterozygotes have no symptoms. At conception, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Kuchtey J. (2011.): Mapping of the disease locus and identification of ADAMTS10 as a candidate gene in a canine model of primary open angle glaucoma. PLoS Genet. 2011;7:e1001306.
Gelatt KN, (2004.): Prevalence of the breed-related glaucomas in pure-bred dogs in North America. Vet Ophthalmol. 2004;7:97–111.
Kuchtey J, Kunkel J, Esson D, et al. (2013.) Screening ADAMTS10 in Dog Populations Supports Gly661Arg as the Glaucoma-Causing Variant in Beagles. Invest Ophthalmol Vis Sci. 2013 Mar 13;54(3):1881-6.