THE ENZYMIC BASIS FOR THE PHENOTYPIC VARIATION OF HURLER AND SCHEIE SYNDROMES

The Hurler and Scheie syndromes are autosomal recessive muco-polysaccharidoses, characterized by mucopolysacchariduria and profound deficiency of α-L-iduronidase when assayed with α-L-phenyl iduronide as substrate. Phenotypically, Hurler patients are severely retarded while Scheie patients have normal intelligence. In order to study the substrate specificity of α-L-iduronidase toward natural substrates, tissue culture techniques were utilized. Skin fibroblasts from patients with Hurler and Scheie syndromes and normal controls were grown to confluency in modified Eagle's medium, washed X 3 with cold NaCl 0.15 M and suspended in 0.05 M acetate in 0.1M Nad buffer pH 3.8. Cells were sonicated then centrifuged at 10,000 × g for 10 min. The supernatant solution was used for α-L-iduronidase activity with substrates prepared from the chemical desulfation of dermatan sulfate and heparin. Following 16 h. of incubation the released iduronic acid was isolated using ion exchange chromatography, and the iduronolactone was identified by paper chromatography. The Hurler cell extracts failed to release iduronic acid from either desulfated heparin or dermatan sulfate while the Scheie extracts released iduronic acid from heparin. Both Hurler and Scheie extracts ha α-L-iduronidase deficiency when assayed with phenyl-iduronide. These findings indicate difference in the α-L-iduronidase specificity toward iduronic acid residues in heparan sulfate, which offers an explanation for the clinical differences between these syndromes.