Murine mucopolysaccharidosis type I: targeted disruption of the murine alpha-L-iduronidase gene.

Mucopolysaccharidosis type I (MPS I) is considered to represent the prototypical mucopolysaccharide storage disorder. Although a spectrum of severity is seen within the MPS I subgroup, Hurler syndrome represents the most severe and frequent manifestation of MPS I. We describe here the generation of a murine model for Hurler syndrome by targeted disruption of the murine Idua gene. Homozygous Idua -/- mice have no detectable alpha-L-iduronidase enzyme activity and show increased urinary glycosaminoglycan levels. Although normal appearing at birth, Idua -/- mice develop a flattened facial profile and thickening of the digits discernible by 3 weeks of age. No obvious growth deficiency nor mortality is seen within the first 20 weeks of life. Radiographs reveal anterior flaring of the ribs and thickening of the facial bones as early as 4 weeks of age with more extensive dysostosis detectable by 15 weeks of age. At 4 weeks of age, lysosomal storage is noted primarily within reticuloendothelial cells with abundant lysosomes noted in Kupffer cells, splenic sinusoidal lining cells, and glial cells. More widespread lysosomal storage is noted by 8 weeks of age in hepatocytes, chondrocytes, neurons, as well as renal tubular cells. Thus, targeted disruption of the murine Idua locus has produced a murine strain representative of the severe form of MPS I. This model should permit detailed evaluation of the pathophysiology of lysosomal storage disorders and provide a small animal model for the testing and development of enzyme replacement and gene therapy regimes.

Mutation analysis of 19 North American mucopolysaccharidosis type I patients: identification of two additional frequent mutations.

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive genetic disorder caused by deficiency of the lysosomal glycosidase alpha-L-iduronidase. Patients with this disorder present with varied clinical phenotypes ranging from early severe onset of disease and death in early childhood to mild manifestations compatible with adult life. An understanding of the molecular basis of iduronidase deficiency and its correlation to clinical phenotype will improve prognostic prediction at diagnosis, aid in genetic counselling of families, and provide a framework to more accurately assess experimental treatment protocols. We have used the approach of single-strand conformational polymorphism analysis and direct sequencing of the alpha-L-iduronidase gene in an attempt to define the molecular basis of iduronidase deficiency in affected individuals. An initial series of 19 patients representing 35 independently segregating mutant alleles were studied. In addition to five previously identified mutations (W402X, Q70X, E274X, H82P, and P533R) two novel mutations (A75T and 474-2a-->g) were found. These seven mutations account for 71% of the mutant alleles and 53% of the genotypes in this group of patients. Analysis of a larger independently ascertained group of 103 MPS I patients, mainly of Northern European origin, revealed that together the two novel mutations account for 7% of mutant alleles and are associated with severe clinical phenotypes. These mutations are the most frequent MPS I mutations detected so far after W402X and Q70X. With the definition of these two mutations, a clear picture of the molecular heterogeneity of MPS I is emerging.