IDENTIFICATION, EXPRESSION, AND BIOCHEMICAL-CHARACTERIZATION OF N-ACETYLGALACTOSAMINE-4-SULFATASE MUTATIONS AND RELATIONSHIP WITH CLINICAL PHENOTYPE IN MPS-VI PATIENTS

Maroteaux-Lamy syndrome, or mucopolysaccharidosis type VI (MPS-VI), is a lysosomal storage disorder characterized by the defective degradati on of dermatan sulfate due to the deficiency of N-acetylgalactosamine- 4-sulfatase (4S). The clinical severity of MPS-VI ranges in a continuu m from mildly affected to severely affected patients. Mutations in MPS -VI patient samples were identified by chemical cleavage and direct DN A sequencing of PCR products derived from patient cDNA. Five amino aci d substitutions were identified (T92M, R95Q, Y210C, H393P, and L498P), individually introduced into the wild-type 4S cDNA by site-directed i n vitro mutagenesis, and transfected into Chinese hamster ovary cells. Three of the five mutations (R95Q, Y210C, and H333P) were observed in >1 of 25 unrelated MPS-VI patients; however, the mutations were not f ound in 20 control individuals. The residual 4S activity and protein ( biochemical phenotype) were determined for each mutant in order to con firm their identity as mutations and to dissect the contribution of ea ch mutant allele to the overall clinical phenotype of the patient. For each patient, the combined biochemical phenotypes of the two 4S mutan t alleles demonstrated a good correspondence with the observed clinica l phenotype (with the possible exception of a patient who was a compou nd heterozygote for T92M and L498P). This preliminary correspondence b etween genotype and the phenotype in MPS-VI may, with further refineme nt, contribute to the assessment of therapeutic approaches for MPS-VI patients.