Goniodysgenesis and Glaucoma Susceptibility
Inheritance: Autosomal recessive
Symptoms: Of glaucoma include severe pain, sensitivity to light, winking spasms, sunken eyes, wincing upon touching dog's head, watery eyes, pain-related behavioral changes, red eye and dilated pupils.
Description:
Glaucoma may be classed as primary (inherited) or secondary (non-inherited) due to other eye conditions (these include inflammation, cataracts, lens luxation, retinal detachment and tumours).
Canine primary closed-angle glaucoma (PCAG), which is the form border collies get, is a complex disease caused by multiple genetic factors. It is an inherited, painful eye disease that is associated with high pressure inside the eye due to reduced drainage of the fluid (aqueous humour). It can cause blindness and needs eye removal to alleviate the pain. A screening technique called gonioscopy can identify dogs at risk.
Goniodysgenesis (aka Pectinate Ligament Dysplasia or Pectinate Ligament Abnormality) is an inherited risk factor for primary closed angle glaucoma in dogs and is an abnormality of the anterior chamber of the eye. The fluid that normally drains out of the eye exits through a drainage angle. With goniodysgenesis, the angle is closed and prevents the fluid of the eye from accessing its exit tract. This can lead to a build up of pressure and possibly gluacoma.
The condition is graded 0-3 based on the severity - the higher the grade the higher the risk of glaucoma.
Importantly, while a diagnosis of goniodysgenesis means the dog is at an increased risk of glaucoma it is not a certainty and many dogs with goniodysgenesis will never develop glaucoma. However, regular eye examinations are recommended to monitor the eye.
The DNA test is a test for goniodysgenesis susceptibility. After a spate of glaucoma affected border collies in related lines in the UK some years ago, the incidence has dramatically decreased. The numbers of affected dogs in Australia is very low. Despite this, the numbers of carriers and at risk dogs from the DNA test are fairly high. For this reason it is recommended that eye testing continues to identify whether at risk dogs will develop glaucoma.
The Kennel Club in the UK has included this information on their Gonio - severe goniodysgenesis/glaucoma web page.
Goniodysgenesis and Glaucoma information sheet - Davies Veterinary Specialists UK
Important note about the DNA Goniodysgenesis susceptibility test
From the published reseach paper (refernce) Whilst most DNA tests definitively identify the gene mutation that causes the disease, sometimes determining this can be difficult. In this case, the mutation identified is strongly associated with severe goniodysgenesis (two copies of the gene were present in nine of 11 affected dogs, and none of 56 unaffected dogs possessed two copies). However, although this association means it is very likely that the identified mutation is the cause of this disorder, it is not absolutely proven that this mutation is entirely and solely responsible for causing the condition, and so is described by The Kennel Club as a ‘very strong contender’ (for being the causal mutation). Despite not being absolutely definitive, this DNA test nevertheless will likely have considerable value in assisting breeding dogs free from the disease.
Because the identified mutation is a ‘very strong candidate’, rather than definitively proven as the only cause of disease, Border Collie breeders should continue to present their dogs for gonioscopy examinations under the British Veterinary Association (BVA)/The Kennel Club (KC)/International Sheep Dog Society (ISDS) Eye Scheme. These eye examination results will provide further data which may assist in proving definitively that the candidate is (or is not) the cause of disease (and if not, in identifying the true cause).
An analysis of data (mid 2023) from the goniodysgenesis/glaucoma and anadune databases indicate that the DNA test is only predicting the development of goniodysgenesis in about 50% of dogs that are homozygous for the mutation. THere are also carriers and clear dogs that are identified with goniodysgenesis. Of the dogs with goniodysgenesis very few develop glaucoma. There appears to be a strong familial link to glaucoma producers. It is advised that a thorough pedigree analysis be conducted prior to making breeding decisions and avoid doubling up on the key glaucoma producing dogs.
The DNA test became available in around 2018.
Border collie glaucoma and goniodysgenesis database