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Mucopolysaccharidosis VI (MPSVI)

Introduction

Mucopolysaccharidosis VI severe (MPSVIs) and mild (MPSVIm) are lysosomal storage diseases resulting from two independent mutations in the gene for enzyme N-acetylgalactosamine 4-sulfatase (4S).  Both are inherited as autosomal recessives, thus males and females can be equally affected if they carry 2 copies of the defective gene. Cats with 2 copies of the severe form show signs at 6-8 weeks of age that include wide faces, shortened noses, small ears, reduced flexibility and retarded growth compared to unaffected littermates.  By 8 months of age, problems of severe hind-limb mobility or paralysis, and signs of degenerative joint disease can be observed. 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. Additional effects of the disease include corneal clouding and heart valve thickening. Cats with two copies of the mild form disease (MPSVIm) have less 4S enzyme and form granules in the white blood cells but otherwise appear healthy.  The same is true of cats with one copy of the mild form and one copy of the severe form. Cats with only one copy (carrier) of either mutation and one copy of the normal gene appear healthy.  Breeding two carriers together is predicted to produce 25% affected offspring and 50% carriers of the disease. Breeds at risk for MPSVIs and MPSVIm are Birman, Ragdoll, Siamese and related breeds, Domestic Shorthair.

The VGL offers DNA tests for MPSVIs and MPSVIm to assist owners and breeders in identifying affected and carrier cats. The tests are done with DNA collected from buccal swabs thus avoiding invasive blood collection.

Procedure for collecting a feline DNA sample

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Allow 2-6 business days for results.

Results reportd as:

Test Result MPSVIs and MPSVIm
N/N Normal, cat does not have either MPSVIs or MPSVIm mutations
N/MPSVIs Carrier, cat has one copy of MPSVIs mutation but is normal
N/MPSVIm Carrier, cat has one copy of MPSVIm mutation but is normal
MPSVIs/MPSVIs

Affected, cat has 2 copies of MPSVIs (severe form)

MPSVIm/MPSVIm

Affected, cat has 2 copies of MPSVIm (mild form)

MPSVIs/MPSVIm

Cat has one copy each of MPSVIs and MPSVIm but may be otherwise healthy

References:

Yogalingam G, T Litjens, J Bielicki et al. 1996. Feline mucopolysaccharidosis type VI. Characterization of recombinant N-acetylgalactosamine 4-sulfatase and identification of a mutation causing the disease. J. Biol. Chem. 271(44): 27259-27265.

Yogalingam G, JJ Hopwood, A Crawley & DS Anson. 1998. Mild feline mucopolysaccharidosis type VI. Identification of an N-acetylgalactosamine 4-sulfatase mutation causing instability and increased specific activity. J. Biol. Chem. 273(22):13421-13429.

Crawley AC, G Yogalingam, VJ Muller & J Hopwood. 1998. Two mutations within a feline mucopolysaccharidosistType VI colony cause three different clinical phenotypes. J. Clin. Invest. 101(1):109-119.

Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL