The Hurler syndrome: detection of patients and heterozygotes using a microassay for alpha-L-iduronidase in fibroblasts.

The activities of alpha-L-iduronidase (EC 3.2.1.76) were measured, by a microassay with phenyl-alpha-L-iduronide as the substrate, in cultured fibroblasts from patients with the Hurler syndrome (MPS IH) or the Scheie syndrome (MPS IS) and from heterozygotes.l The iduronidase activities in the cells from 44 MPS IH and 7 MPS IS patients were all strongly reduced and distinct from the activities in heterozygotes and normal controls. In a group of 24 obligate heterozygotes for MPS IH, 23 could be classified as heterozygotes when the average iduronidase activities of two independent assays were considered. The use of a standard enzyme preparation as a reference in the assays further improved the identification of heterozygosity. The testing of possible heterozygotes (relatives of patients) and their partners may be a valuable contribution in genetic counselling.