Abstract

ASSAY OF α – L – IDURONIDASE AND DETECTION OF MUCOPOLYSACCHARIDOSIS I A REPORT IN SOUTH INDIAN POPULATION

Priya Sundarrajan* and R. Maya Sundari

Abstract

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive, progressive, multi system lysosomal storage disorder caused by mutations in the α – L – Iduronidase (IDUA) gene. These mutations lead to the deficiency of the glycosidase, α – L – Iduronidase (IDUA), which is required for the degradation of the glycosaminoglycans (GAGs) heparan sulphate and dermatan sulphate and hence, their storage in the lysosomes. At present the disease is not curable and has overlapping clinical features with other lysosomal disorders, hence definitive confirmation with enzyme assay is the service most often requested by the affected families, second only to the demand for effective therapy. The present study is a report of a study undertaken in this perspective, in south Indian population. 102 clinically diagnosed patients were biochemically analysed by urinary glycosaminoglycan levels. Of these, 11 patients were confirmed to be MPS I as they showed very low or almost nil activity of IDUA in their leukocytes ie 0.3± 0.6 nmol/hr/mg protein when compared to the activity of IDUA in leukocytes of 34 controls (14 adults and 20 children) who were found to have a mean specific activity of 27.2± 7.5 nmol/hr/mg protein in adults and 30.1± 9.7 nmol/hr/mg protein in children. The levels of the enzyme in 18 obligate heterozygotes were estimated and the mean specific activity was found to be 9.17± 4.07 nmol/hr/mg protein which was found to be little less than 50% of the mean in controls indicating their carrier status. Hence assay of IDUA in leukocytes of patients can be used for the definitive diagnosis of MPS I patients and an indication of carrier status of the heterozygotes. This is one of the first reports in south Indian population.

Keywords: Mucopolysaccharidosis I, Lysosomal storage disorder, Glycosaminoglycans, ? – L – Iduronidase, Carrier status.