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.

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IntroductionFanconi anemia (FA) is an autosomal recessive disease of childhood characterized by progressive pancytopenia, various developmental abnormalities, and a predisposition to acute myeloid leukemia. 1 Most individuals with FA, however, succumb to the complications of aplastic anemia. 2 FA cells demonstrate increased sensitivity to DNA cross-linking agents such as mitomycin C (MMC), diepoxybutane, and cisplatin, 2,3 a feature that serves as the basis for an important diagnostic test. FA cells treated with these cross-linking agents show a striking increase in double-strand DNA breaks and inhibited growth with cell cycle arrest in G 2 . 2 To date at least 7 potential FA genes have been indicated by complementation studies, and most of these genes, FANCA, FANCC, FANCD2, FANCE, FANCF, and FANCG, whose mutations account for 6 of the complementation groups, have now been characterized. [4][5][6][7][8][9][10] Despite the variety of genes involved in this disorder, mutations in FANCA and FANCC account for approximately 80% of all patients with FA. 11 Murine Fancc, being highly similar to the human ortholog, is able to complement human cells deficient in FANCC, restoring MMC resistance. 12 Fancc-deficient mouse strains were generated through gene targeting. Both had similar phenotypes, 13,14 demonstrating compromised gametogenesis, and an increase in the number of chromosomal aberrations, both spontaneously and after exposure to MMC. However, the targeted lines recapitulated neither the developmental nor the hematologic defects typical of human FA. 13,14 The reason for this interspecies discordance is unknown, but it has limited the utility of the mutant mice as potential models of FA.A number of hypotheses regarding the nature of the primary defect in FA have been suggested, including the proposal that FA proteins constitute a DNA damage recognition and signaling pathway, whose impairment is manifested by chromosomal instability and increased sensitivity to interstrand DNA cross-linking agents. 15 Although a reduced ability to process DNA cross-links is clearly evident, it has also been proposed that an abnormal reduction of MMC in FA cells leads to the production of reactive species that in turn generate cross-links and other types of oxidative lesions. 16 Thus, FA might also result, at least in part, from an abnormal regulation of cell redox state or of the cellular response to oxidative stress or both. In support of this notion, addition of Cu/Zn superoxide dimutase (SOD) to the culture medium of FA cells was reported to attenuate chromosomal breakage as well as MMC cytotoxicity, 16 an effect also observed in FA cells overexpressing thioredoxin. 17 In keeping with an inability to regulate either production, or the consequences of reactive oxygen species (ROS), some FA cells were shown to be hypersensitive to oxygen. 16,18 Thus, cells grew slowly at elevated oxygen levels (eg, 35%) and For personal use only. on May 9, 2018. by guest www.bloodjournal.org From tended to arrest at G 2 , whereas at low oxygen conc...