Mucopolysaccharidosis (MPS) is a group of lysosomal storage diseases that are inherited as an autosomal recessive trait. These are classified as:
- MPS I – α-L-iduronidase deficiency, reported in domestic shorthair cats
- MPS VI – arylsulphatase B deficiency, reported in Siamese and domestic shorthair cats – this is one of the most commonly identified lysosomal storage disorders in cats
MPS leads to an accumulation of glycosaminoglycans within numerous cells of the body, including liver, skin, muscle, bone marrow and white blood cells. Clinical signs include:
- Reduced growth rate
- Skeletal deformity – flattened face with widely spaced eyes and small ears
- Stunted growth and skeletal abnormalities
- Enlarged liver
- Cloudy discolouration of the corneas (usually clear areas at the front of the eyes appear cloudy)
- Mental retardation may also be evident
Signs are usually evident from 6-8 weeks, with the skeletal deformities giving rise to a crouching gait. Joints may be painful to manipulate, and compression of the spinal cord can lead to hindlimb weakness or paralysis. Bony changes progress up to about 9 months of age then may stabilise.
Diagnosis may be based on radiographic changes to the bones, granules and vacuoles in peripheral white blood cells and a positive toludine blue ‘spot’ test in urine.
Different DNA mutations may cause varying severity of clinical signs.