Primary Open Angle Glaucoma/Primary Lens Luxation (Shar Pei type)

Find out if your Shar Pei could develop Primary Open Angle Glaucoma (POAG) or Primary Lens Luxation (PLL) caused by ADAMTS17 at CAGT.

UK only
CODE POAG3-ADAMTS17
Categories ,
Breed(s)
Aliases , ,

Results from this test will be reported as detailed in the Registry Reporting list.

Overview

Both primary lens luxation (PLL) and primary open angle glaucoma (POAG) have been diagnosed in Shar Pei that are homozygous (carry two copies) for the 6 bp deletion in ADAMTS17 . Currently it remains unclear whether this single mutation can indeed cause both PLL and POAG, or whether the mutation causes POAG and the fact that both POAG and PLL have been diagnosed in dogs that are homozygous for the mutation is that it can be difficult to differentiate between the two conditions (because POAG can lead to secondary lens luxation and PLL can lead to secondary glaucoma). As a result, until POAG and PLL in Shar-Pei can be further characterized, we suggest they might be considered together as POAG-PLL in this breed.

Th early clinical signs of primary open angle glaucoma (POAG) can be detected by a veterinary ophthalmologist when dogs are between 3 and 4 years of age. The initial signs are a small, sustained rise in intraocular pressure (IOP) and lens subluxation. Unlike primary closed angle glaucoma, which is the more common form of glaucoma in dogs, there is no pectinate ligament abnormality and the iridocorneal angle remains open until the late stages of the disease. POAG is not painful in its early stages and the slow progression of this disease means that often owners are not aware their dog is affected until they notice their dogs’ eyes have become enlarged (due to the increased pressure) or a vision problem becomes noticeable. POAG is progressive, however, and the continued rise in IOP will eventually lead to pain and blindness.

PLL is the term given to the spontaneous displacement or movement of the lens from its normal position within the eye, as a result of rupture of the lens zonules that hold the lens in its normal position. The zonules are a network of tiny fibres that attach the edge of the lens to the ciliary muscle that circles the eye, in the same way that springs attach a trampoline to its frame. Following zonule rupture the lens usually moves to the anterior chamber at the front to the eye where it can cause damage and rapid onset glaucoma by obstructing the drainage of fluid out of the eye resulting in an increase of pressure within the eye. Glaucoma can cause irreversible vision loss if not treated quickly. PLL is invariably bilateral (occurs in both eyes), although a period of several weeks or months might separate luxation of the two lenses. Clinical signs of PLL include sudden onset of eye pain, clouding of the cornea (the front of the eye will look blue), redness of the “white” of the eye and a reluctance to exercise. PLL should be considered an emergency and veterinary assistance sought immediately.

Autosomal Recessive

The 6bp deletion in ADAMTS17 that causes POAG-PLL in Shar pei is recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop POAG-PLL during their lives. Dogs that carry a single copy of the inversion (also known as carriers or heterozygotes) will not develop POAG-PLL as a result of the ADAMTS17 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop POAG-PLL should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.

Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the ADAMTS17 6bp deletion (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with POAG-PLL, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.

Genetic tests are only able to detect specific mutations or variants that have been previously identified. New eye diseases emerge within breeds from time to time and for this reason we recommend that all breeding dogs have their eyes clinically examined by a veterinary ophthalmologist within the twelve months prior to breeding, regardless of the availability of genetic tests for eye diseases that are known to affect the breed. This will help identify new eye diseases before the become widespread. We also recommend that breeding dogs have their eyes examined when they reach eight years of age, to detect any late onset eye diseases that had not developed at the time they were bred.

Gene ADAMTS17
Variant 6-bp (CGTGGT) deletion in exon 22
Assay Type Variant Specific
Inheritance Autosomal Recessive
Severity Moderate-Severe: The welfare of affected animals is significantly affected and life expectancy is usually reduced.
Publication

1. Oliver JAC, Rustidge S, Pettitt L, et al. (2018) Evaluation of ADAMTS17 in Chinese Shar-Pei with primary open-angle glaucoma, primary lens luxation, or both. Am J Vet Res. 79(1): 98-106. DOI: 10.2460/ajvr.79.1.98.

2. Lazarus JA, Pickett JP and Champagne ES et al. (1998) Primary lens luxation in the Chinese Shar Pei: clinical and hereditary characteristics. Vet Ophthalmol. 1(2-3): 101-107. DOI: 10.1046/j.1463-5224.1998.00021.x..