Molecular test for X-linked progressive retinal atrophy (XL-PRA), an inherited retinal degeneration that leads to progressive blindness in hemizygous males and homozygous females. It affects the ocular system (photoreceptors) and forces the animal to adapt to gradual visual loss. The test reports clear/carrier/affected status for the corresponding variant.

Applicable breeds: Siberian Husky and Samoyed. Carrier frequencies (females) are not published systematically (limited data); the clinical casuistry is known in both breeds and should be verified in the specific literature.

- Reduced night vision at onset\n- Progressive bilateral retinal atrophy\n- Complete blindness in advanced stages\n- Fundus changes: tapetal hyperreflectivity and vascular attenuation\n- Affected males with typical progression; carrier females generally asymptomatic

XL-PRA was described in the Siberian Husky and Samoyed (XLPRA1) as a form of PRA with X-linked recessive inheritance. Zhang et al. (2002) characterised the molecular cause: a 5-bp deletion (delGAGAA) in the ORF15 region of the RPGR gene (retinitis pigmentosa GTPase regulator), related to the mutations of human X-linked retinitis pigmentosa. Other RPGR variants cause XLPRA2 (more severe, with developmental onset) and XLPRA3.

- Genotype breeding dogs before mating\n- Due to X-linked inheritance: carrier females transmit the variant to 50% of daughters (carriers) and 50% of sons (50% of the males will be affected); affected males should not be bred\n- To reduce the frequency of the variant, do not breed with carrier females; if they are mated, the male offspring in the litter intended for breeding should be clear\n- Do not mate a carrier female with an affected male (risk of affected homozygous daughters)\n- After a confirmed clinical case, do not repeat the parental mating and inform the buyer of the status

Complementary annual eye examination (ECVO) to confirm the disease and follow its progression. Differentiate XL-PRA from other recessive PRAs (prcd-PRA, rcd1-rcd3, Cord1) by inheritance pattern (X-linked, typically only males affected), age at onset and fundus. Molecular confirmation is especially useful in breeding females to avoid transmitting the variant to affected offspring.

1. Zhang Q, Acland GM, Wu WX, Johnson JL, Pearce-Kelling S, Tulloch B, Vervoort R, Wright AF, Aguirre GD. 2002. Different RPGR exon ORF15 mutations in Canids provide insights into photoreceptor cell degeneration. Hum Mol Genet 11:993-1003. PMID: 11978759
2. OMIA:000831-9615. Retinal atrophy, progressive, X-linked, type 1 (XLPRA1), RPGR-related, perro.