PRA in Shih-Tzu

Progressive retinal atrophy (PRA) is a large group of hereditary diseases that are the leading cause of blindness in various dog breeds. Individuals affected by PRA exhibit a similar sequence of clinical abnormalities throughout the course of the disease. Symptoms begin with night blindness, followed by gradual loss of daytime vision and eventual blindness in all light conditions. Routine eye examinations reveal a gradual loss of light-sensitive cells in the retina due to degeneration or atrophy of the retina, which gives the disease its name.

In the Shih Tzu breed, the disease is associated with a nonsense mutation c.452A>C in the JPH2 (junctophilin-2) gene, which ensures the connection of membranes in photoreceptors and the regulation of calcium signalling pathways.

The mutation is inherited in an autosomal recessive manner. It only manifests itself in individuals who have inherited the mutated allele from both parents (recessive homozygotes). Heterozygotes are individuals who have inherited the mutated allele from only one parent, show no symptoms of the disease, and are clinically healthy. However, they can pass the mutated allele on to their offspring. If two heterozygous individuals mate, theoretically 25% of their offspring will be completely healthy, 50% will be carriers, and 25% will inherit the mutated allele from both parents and will therefore be affected by PRA4.

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Reference:

Urkasemsin, G., Pongpanich, M., Sariya, L., Kongcharoen, A., Buddhirongawatr, R., Rungarunlert, S., Ferreira, J.N., Chetruengchai, W., Phokaew, C., Srichomthong, C., Shotelersuk, V. : Whole genome sequencing identifies a homozygous nonsense mutation in the JPH2 gene in Shih Tzu dogs with progressive retinal atrophy. Anim Genet 52:714-719, 2021. Pubmed reference: 34231238