Mild feline mucopolysaccharidosis type VI. Identification of an N-acetylgalactosamine-4-sulfatase mutation causing instability and increased specific activity.
The missense mutation, L476P, in the N-acetylgalactosamine 4-sulfatase (4S) gene, has previously been shown to be associated with a severe feline mucopolysaccharidosis type VI (MPS VI) phenotype. The present study describes a second mutation, D520N, in the same MPS VI cat colony, which is inherited independently of L476P and is associated with a clinically mild MPS VI phenotype in D520N/L476P compound heterozygous cats. Biochemical and clinical assessment of L476P homozygous, D520N/L476P compound heterozygous, and D520N homozygous cats demonstrated that the entire range of clinical phenotypes, from severe MPS VI, to mild MPS VI, to normal are clustered within a narrow range of residual 4S activity from 0. 5% to 4.6% of normal levels. When overexpressed in CHO-KI cells, the secreted form of D520N 4S was inactivated in neutral pH conditions. In addition, intracellular D520N 4S protein was rapidly degraded and corresponded to 37%, 14.5%, and 0.67% of normal 4S protein levels in the microsomal, endosomal, and lysosomal compartments, respectively. However, the specific activity of lysosomal D520N 4S was elevated 22. 5-fold when compared with wild-type 4S. These results suggest that the D520N mutation causes a rapid degradation of 4S protein. The effect of this is partially ameliorated as a result of a significant elevation in the specific activity of mutant D520N 4S reaching the lysosomal compartment.
Yogalingam
G
G
Lysosomal Diseases Research Unit, Department of Chemical Pathology, Women's and Children's Hospital, 72 King William Road, North Adelaide, South Australia 5006, Australia.
Hopwood
J J
JJ
Crawley
A
A
Anson
D S
DS
D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002415:Cats; D002803:Chondro-4-Sulfatase / Q000235:genetics*; D006224:Cricetinae; D004705:Endocytosis; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism; D005838:Genotype; D006025:Glycosaminoglycans / Q000378:metabolism; D006579:Heterozygote; D006720:Homozygote; D009087:Mucopolysaccharidosis VI / Q000201:enzymology / Q000235:genetics*; D009154:Mutation; D010641:Phenotype; D012867:Skin / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D013347:Subcellular Fractions / Q000201:enzymology
D006025:Glycosaminoglycans; D002803:Chondro-4-Sulfatase