Mucopolysaccharidosis type VI (MPS VI) is a lysosomal storage disease that is triggered by two independent mutations in the gene for enzyme N-acetylgalactosamine 4-sulfatase (4S). Both mutations are autosomal and recessive. The two mutations occur separately leading to the presence of six possible genotypes. The two mutations have different effects on the severity of the disease. A mild form (m) and a severe form (s), the mild form may only be detected by certain laboratory tests. With the severe form symptoms starts at 6-8 weeks of age and includes wide face, shortened nose, small ears, reduced flexibility and retarded growth compared to unaffected littermates. By 8 months of age, affected cats suffer of severe hind-limb mobility problems or paralysis, neurological symptoms and dwarfism. Clinically, urine samples show increased levels of dermatan sulfate (DS) and an increase in white blood cell granules. Organs and tissues can also be compromised by accumulation of intercellular DS.
Symptoms may include:
- Abnormal facial structure
- Widespread cloudiness of the cornea (Diffuse corneal clouding)
- Sunken chest (pectus excavatum)
- Granulation of white blood cells in the peripheral blood
- Abnormal development of the growth plates (epiphyseal dysplasia)
- Irregular bone formation (ossification)
- Short stature (dwarfism)
- Joint degeneration
- Arthritis of the spine (spondylosis)
- Dislocation of the hip and thigh (coxofemoral subluxation)
- Partial dislocation of the kneecap (patellar subluxation)
It seems that cats with one copy of the severe and one copy of the mild form are unlikley to show symptoms.
The severe mutation: s
The mild mutation: m
Possible genotypes:
N/N Normal, cat does not have either the server or the mild mutations
N/s Carrier, cat has one copy of severe mutation but is healthy
N/m Carrier, cat has one copy of MPSVIm mutation but is healthy
s/s Affected, cat has 2 copies of the severe S mutation
m/m Affected, cat has 2 copies of the mutation
m/s Cat has one copy each of the severe and one copy of the mild mutation but may be otherwise healthy
