Mucopolysaccharidosis type I: clinical and biochemical study.

Of 1240 outpatients referred to the Human Genetics Clinic between 1997 and 1998, 248 (20%) had inborn errors of metabolism, 36 (14%) of which were diagnosed as mucopolysaccharidoses. Parental consanguinity was present in 82% of these patients. Deficiency of alpha-L-iduronidase (IDUA) enzyme in leukocytes and increased urinary mucopolysaccharides excretion were detected in 17 patients. The urinary spot test for glucosaminoglycans was inconclusive in 4 of the 17 cases. Results showed a correlation between the biochemical enzyme activity in leukocytes, the amount of excreted mucopolysaccharides and the subtype and course of mucopolysaccharidosis type I. We conclude that estimation of IDUA enzyme activity in leukocytes can differentiate between clinically overlapping cases of MPS I and MPS II and given the clinical manifestations of MPS I is a definitive and unequivocal method of diagnosis while the urinary spot test is inconclusive.