Hurler syndrome: alpha-L-iduronidase activity in leukocytes as a method for heterozygote detection.

Alpha-L-Iduronidase activity and beta-galactosidase activity were determined in mixed leukocyte preparations in 10 families in which the Hurler syndrome had occurred. Affected patients, heterozygotes, and normal subjects were clearly distinguished by alpha-L-iduronidase activity alone. Patients had 0-3%, obligate heterozygotes 19-60%, and normal subjects 83-121% of the mean normal activity. There was no overlap between heterozygotes and normal subjects. Although the mean alpha-L-iduronidase to beta-galactosidase ratio was significantly lowered in heterozygotes when compared with that of normal subjects, appreciable overlap was noted between the two groups.