Primary Congenital Glaucoma

Primary congenital glaucoma in cats is characterized by elevated intraocular pressure from an early age, which can result in significant ocular damage. The genetic variant associated with the disorder has been located in the LTBP2 gene, which encodes a relevant protein in the extracellular matrix.

Symptoms

The disease in cats manifests clinically as mild to moderate bilateral enlargement of the eyeballs, observable from the first weeks of life. From 8 weeks of age onwards, affected cats show significantly increased intraocular pressure. Other clinical signs include prominent and elongated ciliary processes, incomplete iris development and iris tremor. In addition, between 4 months and two years of age, some cats may have lens subluxation or luxation, and corneal edema in less than 10% of cases. Optic nerve damage is also observed from 6 months of age.

Disease Management

Currently, there is no definitive cure for glaucoma. Treatment focuses on relieving clinical symptoms by using eye drops that reduce intraocular pressure and steroids to treat inflammation. In severe cases, surgical removal of one or both eyes may be considered if pain cannot be controlled otherwise.

Genetic basis

This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the cat, regardless of sex, must receive two copies of the mutation or pathogenic variant to be at risk of developing the disease. Both parents of an affected cat must carry at least one copy of the mutation. Animals with only one copy of the mutation are not at increased risk of developing the disease, but may pass the mutation on to future generations. Breeding between cats carrying genetic variants that may cause disease is not recommended, even if they do not show symptoms.

Technical report

Glaucoma is a group of diseases that cause damage to the optic nerve, being one of the main causes of blindness in both pets and humans. In Siamese cats, this condition is related to a mutation in the LTBP2 (latent transforming growth factor beta binding protein 2) gene, which encodes an extracellular matrix protein. The mutation involves the insertion of 4 base pairs in exon 8 of the gene, which causes a change in the reading frame and leads to premature truncation of the protein. This effect interferes with the proper assembly of the microfibrils in the extracellular matrix, thus affecting the flow of aqueous humor and leading to the development of glaucoma.

Most affected breeds

Siamese

Bibliography

Kuehn MH, Lipsett KA, Menotti-Raymond M, et al. Mutation in LTBP2 Causes Congenital Glaucoma in Domestic Cats (Felis catus). PLoS One. 2016 May 5