Primary open angle glaucoma in Petit Basset Griffon Vendéen (POAG)

Glaucoma is a heterogeneous group of disorders that lead to blindness due to the death of retinal ganglion cells and damage to the optic nerve. It is the most common cause of the blindness and visual impairment in humans and dogs worldwide (Bouhenni et al., 2012). In general, the glaucoma is classified as primary (in most cases inherited) and secondary (acquired due to eye damage - e.g. injury, tumour and others) (Kotman et al., 2003).

The primary glaucoma is sub-divided in three groups by the iridocorneal angle (the angle between the iris, the cornea and the white):

• Primary open angle glaucoma (POAG)
• Primary angle closure glaucoma (PACG)
• Primary congenital glaucoma (PCG)

POAG in small wiry-haired Basset Vendeen is caused by mutation in ADAMTS17 gene. It is an inversion mutation during which a part of chromosome breaks away and reattaches in a reversed order. The ADAMTS17 gene is a member of the ADAMTS family of extracellular proteases. The mutation probably disrupts the enzymatic function of the protein.

The disease is characterized by a small, sustained rise in intraocular pressure and lens subluxation. The initial clinical signs occur in 3 to 4-year-old dogs of either sex. The so-called aphakic crescent (half-moon) connected with lens subluxation occurs in approximately one third of the affected dogs. In the late stage of the disease, globe enlargement develops. Retina degeneration and cupping deformation of the optic papilla can be seen only in late disease.   Pain is not a feature of this type of disease and so the owners of the affected dogs become aware of the presence of POAG when either the glove enlargement or a vision problem becomes noticeable.

Mutation that causes POAG in Petit Basset Griffon Vendéen is inherited as an autosomal recessive trait. That means the disease affects dogs with P/P (positive / positive) genotype only. The dogs with P/N (positive /negative) genotype are clinically without any symptom. They are genetically considered carriers of the disease (heterozygotes). In offspring of two heterozygous animals following genotype distribution can be expected: 25 % N/N (healthy non-carriers), 25 % P/P (affected), and 50 % N/P (healthy carriers). Because of high risk of producing affected offspring, mating of two N/P animals (carriers) can not be recommended.

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Reference:

A. BOUHENNI, Rachida, Jeffrey DUNMIRE, Abby SEWELL a Deepak P. EDWARD. Animal Models of Glaucoma. Journal of Biomedicine and Biotechnology. 2012, vol. 2012, s. 1-11. DOI: 10.1155/2012/692609. Dostupné z:http://www.hindawi.com/journals/bmri/2012/692609/

KOTTMAN J, Raušer P, Kecová H, Trnková P, Krisová Š. Veterinární oftalmologie. 1. vyd. Brno: Noviko, 2003, 198 s.

Bedford, P.G.: Open-angle glaucoma in the Petit Basset Griffon Vendeen. Vet Ophthalmol 20:98-102, 2017. Pubmed reference: 26945802