Mucopolysaccharidosis type VII (Sly disease) is a hereditary lysosomal disease caused by beta-glucuronidase deficiency, which leads to the accumulation of glycosaminoglycans in tissues. In the cat it affects the skeleton, the cornea and the internal organs, with growth retardation, bone deformities and corneal opacity, in a picture similar to that of other mucopolysaccharidoses. It is progressive, with no curative treatment in clinical practice, and its control is based on avoiding matings between carriers.

Exceptional disease in the cat; the test is offered for all breeds. There are no published carrier frequencies: limited data.

- Growth retardation and small size
- Coarse facial features with a broad head
- Bilateral corneal opacity
- Joint stiffness and skeletal deformities
- Possible hepatomegaly in advanced cases
- General progressive deterioration with reduced life expectancy

Natural MPS VII was described in the domestic cat with beta-glucuronidase deficiency. Fyfe et al. (1999) identified the molecular basis (missense variant E351K in GUSB) and Wang et al. (2015) described a second causal mutation in a domestic shorthair cat: two adjacent transitions in exon 9, one of which had already been identified in human patients. The feline model has been valuable for the study of therapies for the human disease. Its occurrence is sporadic and the specific literature on the cat is scarce.

- Include the test in the screening of breeding animals from lines with previous cases of mucopolysaccharidosis.
- Do not mate two carriers together; a carrier with a clear animal does not produce affected offspring.
- Test offspring intended for breeding and record the results.
- In the presence of compatible signs (dwarfism, corneal opacity, stiffness), complete the study with the other MPS in the panel.

Differential diagnosis with MPS VI and other storage diseases, pituitary dwarfism, congenital hypothyroidism and non-genetic corneal opacities. Determination of glycosaminoglycans in urine and the lysosomal enzyme profile help to guide; the genetic test confirms. Coordinate the study with cardiac and abdominal ultrasound in the presence of findings of visceral accumulation.

1. Fyfe JC et al. (1999) Molecular basis of feline beta-glucuronidase deficiency: an animal model of mucopolysaccharidosis VII. Genomics 58:121-8. PMID: 10366443
2. Wang P et al. (2015) Mucopolysaccharidosis VII in a Cat Caused by 2 Adjacent Missense Mutations in the GUSB Gene. J Vet Intern Med 29:1022-8. PMID: 26118695
3. Lyons LA (2015) DNA mutations of the cat: the good, the bad and the ugly. J Feline Med Surg 17:203-19. PMID: 25701860
4. OMIA:000667-9685. Mucopolysaccharidosis VII in Felis catus. https://omia.org/OMIA000667/9685/