N-acetylglucosamine-6-sulfate sulfatase in man: deficiency of the enzyme in a new mucopolysaccharidosis.

Abstract

Summary: The study of a 5-year old patient with a mucopolysaccharidosis different from those already known has given the opportunity to describe the clinical, biochemical and enzymic characteristics of JV-acetylglucosamine-6-sulfate sulfatase deficiency.The patient was delayed physically and mentally, was hyperactive, and had a short attention span. He had fair complexion and very blond, but coarse and excessive hair. He had mild hepato-splenomegaly and dysostosis multiplex, including hypoplastic odontoid process of the atlas, ovoid vertebral bodies, small femoral epiphyses, and modest enlargement of the ribs. He had a mild, bilateral conductive hearing loss. The urine gave a strongly positive spot test with Azur A paper. Quantitative measurement of urinary glycosaminoglycans demonstrated increased excretion and inadequate degradation of heparan sulfate and keratan sulfate. The microscopic examination of the stained peripheral leukocytes revealed metachromatic material which formed a ring on the inner aspect of the cellular membrane in 20% of the lymphocytes. The rate of degradation of 35SO4-labeled intracellular glycosaminoglycans by cutaneous fibroblasts was delayed and inadequate.The measurements of several lysosomal enzymes whose deficiencies are responsible for the known mucopolysaccharidoses gave results within normal ranges. GaIactose-6-sulfate (Gal-6-S), N-acetylgalactosamine-6-sulfate (GalNAc-6-S), and N-acetylglu-cosamine-6-sulfate (GlcNAc-6-S) were prepared with chlorosulfonic acid, according to the method of Suzuki and Strominger (38). After chromatographic purification, aliquots of the three 6-sulfated monosaccharides were reduced with sodium borotritide. Measurements of Gal-6-S sulfatase, GalNAc-6-S sulfatase, and GlcNAc-6-S sulfatase were performed on extracts of normal cultured fibroblasts and of fibroblasts of the propositus, his parents, and several Morquio patients. Additionally, GalNAc-6-S sulfatase and GlcNAc-6-S sulfatase activities were also measured, using as substrate 500 nmol tetrasaccharide obtained from either chon-droitin-6-sulfate or nonradioactive GlcNAc-6-S. The measurement demonstrated that the propositus has a defective GlcNAc-6-S sulfatase activity, but normal activities for Gal-6-S and GalNAc-6-S sulfatase.These findings are in contrast with those found with fibroblast extracts of Morquio patients, since they have low or nondetectable activities of Gal-6-S and GalNAc-6-S sulfatase but normal GlcNAc-6-S sulfatase activity.Extracts of leukocytes and fibroblasts of the propositus' parents, when tested with radioactive or nonradioactive substrates, had normal levels of GalNAc-6-S sulfatase activity but decreased levels of GlcNAc-6-S sulfatase activity (50–60% of normal).Speculation: The possible existence of two different sulfatases, specific for 6-sulfated hexoses with the glucose or galactose configuration, has been suggested (10).The study of a patient with a novel mucopolysaccharidosis, characterized by defective degradation of keratan sulfate and heparan sulfate, has provided the opportunity of describing the clinical and biochemical features of GlcNAc-6-S sulfatase deficiency. These findings confirm that the defective degradation of keratan sulfate and chondroitin-6-sulfate typical of classic Morquio disease is caused by the deficiency of a sulfatase specific for Gal-6-S and GalNAc-6-S.