Comparison of the substrate 4-methylumbelliferyl-alpha-l-iduronide with phenyl-alpha-L-iduronide for the diagnosis of Hurler's disease in cultured cells.

4-Methylumbelliferyl-alpha-l-iduronide provided a more sensitive method than phenyl-alpha-l-iduronide for the estimation of alpha-l-iduronidase in cultured cells and could be used to diagnose Hurler's disease. The 4-methylumbelliferyl derivative was no more useful than the phenyl derivative for the detection of heterozygotes. All ten lysosomal enzymes tested could be used as reference enzymes when cell extracts were prepared by freeze/thawing in formate buffer pH 3.5 containing 150 mmol/l sodium chloride.