I'll keep this short as Mucopolysaccharidosis is a complex disease, which also affects humans. In Medical, Genetic & Behavioral Aspects of Purebred cats (Edited by Ross D. Clark, DVM) it is stated as affecting the Siamese cat sometimes.
Mucopolysaccharidosis VI is a disorder affecting metabolism caused by a defective autosomal recessive gene. It causes a deficiency in an enzyme called N-acetylgalactosamine 4-sulfatase (src: Wikipedia); the above book calls the enzyme arylsulfatase B. This results in the storage of long chains of sugar carbohydrates in the cat's cells.
The symptoms are:
- skeletal abnormalities including:
- wides spaced eyes
- small ears
- flattened face
- frontal bossing (prominent forehead)
- kittens at 1o weeks are smaller than normal and have corneal clouding and prolapsed third eyelids. There front are larger than normal. At 5 months they have an abnormal gait.