Primary open angle Glaucoma (POAG) in Basset hounds

Glaucoma is a diverse group of diseases that gradually lead to blindness due to loss of retinal ganglion cells and damage to the optic nerve. It is the most common cause of blindness and visual impairment in humans and animals worldwide (Bouhenni et al., 2012). The disease is characterized by a small but permanent increase in intraocular pressure and subluxation of the lens. In the late stages of the disease, there is enlargement of the eyeball, retinal degeneration and deformation of the optic nerve papilla.

In general, glaucoma is classified as primary (usually hereditary) and secondary disease (resulting from other damage to the eye - e.g. trauma, tumour, etc.) (Kotman et al., 2003).

Primary glaucoma is further subdivided according to the iridocorneal angle (the angle
between the iris, cornea and the white of the eye) into three main groups:

• Primary open angle glaucoma (POAG)
• Primary closed angle glaucoma (PACG)
• Primary Congenital Glaucoma (PCG)

POAG in Basset hounds is caused by the c.194_213del mutation in the ADAMTS17 gene. The ADAMTS17 gene is a member of the ADAMTS family of extracellular proteases. The mutation probably disrupts the enzymatic function of the protein.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected puppies.

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References:

Oliver, J.A., Forman, O.P., Pettitt, L., Mellersh, C.S. : Two independent mutations in ADAMTS17 are associated with primary open angle glaucoma in the Basset Hound and Basset Fauve de Bretagne breeds of dog. PLoS One 10:e0140436, 2015. Pubmed reference: 26474315