Mucopolysaccharidosis Type 1 (MPSI) is a lysosomal storage disease caused by deficient activity of the alpha-L-iduronidase enzyme, which is used to break down dermatan and heparan sulfates. This results in the accumulation of glycosaminoglycans (GAGs) in various types of cells which eventually progresses to cellular damage. The disorder varies from mild to severe, with severe cases carrying a grave prognosis at an early age. Clinical signs typically develop in kittens from eight weeks to six months of age. These signs may include failure to thrive, growth retardation, skeletal deformities, lameness, facial dysmorphism, ataxia, and tremors. Affected cats can also have visually smaller ears than normal cats and thick skin over the dorsal neck. Additionally, some affected cats may show corneal cloudiness and/or have a cardiac murmur due to mitral insufficiency. MPSI follows an autosomal recessive mode of inheritance.

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 mutation are needed for disease signs to be shown. A carrier cat with one copy of the MPS1 mutation can be safely bred with a clear cat with no copies of the MPS1 mutation. About half of the kittens will have one copy (carriers) and half will have no copies of the MPS1 mutation. 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 MPS1 mutation could develop due to a different genetic or clinical cause.