Mucopolysaccharidosis Type VI is a rare lysosomal storage disease caused by deficient activity of the N-acetylgalactosamine-4-sulfatase enzyme, which is used to break down dermatan and chondroitin sulfates. This results in the accumulation of glycosaminoglycans (GAGs) in various types of cells which eventually progresses to cellular damage. The typical form of the disease causes dwarfism, reduced flexibility, facial dysmorphia, corneal clouding, degenerative joint disease, and abnormal leukocyte inclusions (with prominent cytoplasmic granules). Affected cats may also have heart valve thickening. Clinical signs typically first appear in kittens at six to eight weeks of age and affected individuals tend to remain cognitively normal. MPS VI follows an autosomal recessive mode of inheritance. Cats with two copies of this variant (also known as T1427C mutation) exhibit the typical form of the disease as described above. Cats with one copy of the Mucopolysaccharidosis Type VI variant (T1427C mutation) and one copy of the Mucopolysaccharidosis Type VI Modifier variant (often referred to as the G1558A mutation) have an increased risk of presenting with a mild form of the disease, manifesting as degenerative joint disease only.

There is high interest in research for safe and effective treatments of MPS disorders in cats, with options such as enzyme replacement therapy and gene therapy showing promise. At present time, however, the most widely available therapy is limited to supportive care. The lifespan of an affected cat is dependent on severity of the individual's condition, and quality of life should be monitored closely.

There are many responsibilities to consider when breeding cats. Regardless of test results it is important that your cat is in good general health and that you are in a position to care for the kittens if new responsible owners are not found. For first time or novice breeders, advice can be found at most cat registry websites.

This disease is autosomal recessive meaning that two copies of the variant are needed for disease signs to be shown. A cat with one copy of the Mucopolysaccharidosis Type VI variant and zero copies of the Mucopolysaccharidosis Type VI Modifier variant can be safely bred with a clear cat with no copies of these variants. About half of the kittens will have one copy of the Mucopolysaccharidosis Type VI variant and will be considered carriers. Kittens in a litter which is expected to contain carriers should be tested prior to breeding. Carrier to carrier matings are not advised as the resulting litter may contain affected kittens. Please note: It is possible that disease signs similar to the ones caused by the MPSVI variant could develop due to a different genetic or clinical cause.