POAG and PLL in Shar Pei

The primary open angle glaucoma (POAG) and the primary lens luxation (PLL) are two diseases that are both caused by the same mutation and thus are indistinguishable from the genetics point of view.

Primary glaucoma is an inherited eye condition that leads to blindness due to loss of retinal ganglion cells and optic nerve damage.  The primary open angle glaucoma is characterized by reduced drainage of fluid from the eye. This causes a build-up of intraocular pressure which, in turn, leads to pain and blindness.  It is possible to observe enlarged pupils, cornea swelling and scleral congestion. The eyes become markedly enlarged and the lens of the eye becomes wobbly and even falls completely out if its normal position. Most dogs become affected by this congenital eye disease at approximately 4-6 years of age.

The lens luxation is an eye disease connected with lens dislocation and leads generally to loss of vision. The lens is in the eye fixed by the fibres of suspension apparatus and the damage to the suspension apparatus (resulting from injury or congenital mutation) causes lens dislocation. The inherited form is caused by defective fixation of lens fibres – loosening of fibres causes shifting of the lens and results in glaucoma and loss of vision.

The POAG/PLL diseases are caused by mutation in ADAMTS17-gene. It concerns the 6-bp deletion in exon 22 of this gene. The disease shows an autosomal recessive mode of inheritance, which means that two copies of the defective gene (one inherited from each parent) have to be present for a dog to be affected by the disease.  Individuals with one copy of the defective gene and one copy of the normal gene are called carriers.  They show no signs of the disease but can pass the defective gene onto their offspring. When a carrier is crossed with a healthy individual 50 % of the offspring will be carriers and 50 % of the offspring will be healthy.  When two carriers are crossed 50 % of the offspring will be carriers, 25 % will be healthy and 25 % of the offspring will be affected by the disease.  By DNA testing the dog genotype can be identified which helps to eliminate the chance of producing a puppy with this disease.

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Reference:

Fabiana H. G. Farias: Molecular genetic studies of canine inherited diseases, A Dissertation presented to the Faculty of the Graduate School University of Missouri, 2011

James A. C. Oliver, Sophie Rustidge, Louise Pettitt, Christopher A. Jenkins, Fabiana H. G. Farias, Elisabeth A. Giuliano, Cathryn S. Mellersh: A novel ADAMTS17 mutation is associated with primary open angle glaucoma and primary lens luxation in the Shar Pei; The 9th international conference on canine and feline genetics and genomics