Diagnosis of Sanfilippo type A syndrome by estimation of sulfamidase activity using a radiolabelled tetrasaccharide substrate.

1. A radiolabelled tetrasaccharide mixture (GlcNS-UA-GlcNS-UOA) containing GlcNSO3-UA-GlcNSO3-L-[6, 3H]idonic acid, GlcNSO3-UA-GlcNSO3-anhydro-L-[6, 3H]idonic acid and GlcNSO3-UA-GlcNSO3-L-[6, 3H]gulonic acid was evaluated together with a radiolabelled disaccharide O-(alpha-2-sulfamino-2-deoxy-D-glucopyranosyl)-(1 leads to 3)-L-[6, 3 H]idonic acid (GlcNS-IdOA) and a trisaccharide GlcNSO3-UA-D-[1, 3 H]glucosaminitol N-sulfate (GlcNS-UA-GlcitolNS) as diagnostic substrates for sulfamidase present in cultured human skin fibroblasts and leucocytes. 2. Sulfamidase activity assessed with GlcNS-UA-GlcNS-UOA was up to 10 times higher than the value obtained for GlcNS-IdOA and the trisaccharide. These results demonstrate that an adjacent GlcNS-UOA disaccharide residue to the sulfaminoglucosamine under attack may play a role in the mechanism of action or binding of sulfamidase toward its substrates. 3. Sulfamidase activity in fibroblast and leucocyte homogenates with GlcNS-UA-GlcNS-UOA exhibited a pH optimum at pH 5.0, an apparent Km of 27 to 50 mumol/l and inhibition by both NaCl and Na2SO4. 4. No detectable sulfamidase activity toward the tetrasaccharide, trisaccharide and disaccharide substrates could be detected using homogenates of fibroblast cultures from Sanfilippo A patients (sulfamidase deficient). Sulfamidase activity assayed with GlcNS-UA-GlcNS-UOA clearly distinguished Sanfilippo A patients from normal controls, heterozygotes and other mucopolysaccharidosis types. Because of the higher activity of sulfamidase toward the tetrasaccharide substrate, compared to that observed for the other substrates evaluated, we recommend its use for the routine enzymic detection of the Sanfilippo A syndrome.