Identification and molecular characterization of mutations in the Alpha-L-Iduronidase gene responsible for mucopolysaccharidosis type 1

Abstract

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive metabolic disease caused by a deficiency of lysosomal alpha-L-iduronidase (IDUA) resulting in an accumulation of partially degraded glycosaminoglycans inside lysosomes. We described two Thai patients with clinical features consistent with MPS I and performed biochemical and mutation analysis. An assay for IDUA activity was carried out in leukocyte extracts using 4-methylumbelliferyl-alpha-L-iduronidase as a substrate. The IDUA activity in a patient with MPS I was less than that of the unaffected controls. Mutation analysis by PCR-sequencing of the entire coding region of the IDUA gene revealed two different potential pathogenic mutations, c.252insC and c.826G>A (p.E276K). The c.252insC found in our patient with Hurler syndrome has been identified in patients with similar phenotype. The p.E276K mutation has never been previously described. We further explored its functional property in cells transiently transfected with the p.E276K construct. The p.E276K exhibited a significant reduction of alpha-L-iduronidase activity compared to that of the wild-type IDUA suggesting it as a disease-causing mutation. This study has further expanded the genotypic spectrum of IDUA as well as emphasized an important role of biochemical and molecular testings for definite diagnosis and genetic counseling.