The mucopolysaccharidoses (MPSs) are inherited lysosomal storage disorders caused by the absence of functional enzymes that contribute to the degradation of glycosaminoglycans (GAGs). The progressive systemic deposition of GAGs results in multi-organ system dysfunction that varies with the particular GAG deposited and the specific enzyme mutation(s) present. Cardiac involvement has been reported in all MPS syndromes and is a common and early feature, particularly for those with MPS I, II, and VI. Cardiac valve thickening, dysfunction (more severe for left-sided than for right-sided valves), and hypertrophy are commonly present; conduction abnormalities, coronary artery and other vascular involvement may also occur. Cardiac disease emerges silently and contributes significantly to early mortality.The clinical examination of individuals with MPS is often difficult due to physical and, sometimes, intellectual patient limitations. The absence of precordial murmurs does not exclude the presence of cardiac disease. Echocardiography and electrocardiography are key diagnostic techniques for evaluation of valves, ventricular dimensions and function, which are recommended on a regular basis. The optimal technique for evaluation of coronary artery involvement remains unsettled.Standard medical and surgical techniques can be modified for MPS patients, and systemic therapies such as hematopoietic stem cell transplantation and enzyme replacement therapy (ERT) may alter overall disease progression with regression of ventricular hypertrophy and maintenance of ventricular function. Cardiac valve disease is usually unresponsive or, at best, stabilized, although ERT within the first few months of life may prevent valve involvement, a fact that emphasizes the importance of early diagnosis and treatment in MPS.

One approach to gene therapy for hepatic diseass is to remove hepatocytes from an affected individual, genetically alter them in vitro, and reimplant them into a receptive locus. Although returning hepatocytes to the liver itself would be advantageous, the feasibility of this approach has never been evaluated due to the inability to distinguish donor from host hepatocytes. To unambiguously identify transplanted hepatocytes after transplantation, and to better quantitate their number and degree of liver function, two transgenic mouse lines were generated in a C57BL/6 background. The first expresses the Escherichia cofi p-galactosidase gene from the relatively liver-specific human a1-antitrypsin (hAAT) promoter and allows transgenic hepatocytes to be readily identified after 5-bromo-4-chloro-3-indolyl .8-D-galactoside staining; the second produces the hAAT protein under control of the same promoter, which enables hepatocyte survival and maintenance of liver function to be quantitated by measuring the serum levels of hAAT. Hepatocytes isolated from transgenic donors were transplanted into nontransgenic C57BL/6 recipients by intrasplenic injection. Surprisingly, a large fraction of these cells were identified within the liver parenchyma but not the spleen at 2 months after transplantation. The high levels of serum hAAT detected in transplant recipients were stable for >6 months, suggesting that established cells will survive indefinitely. These results have important implications for liver organogenesis and hepatic gene therapy.

Type I mucopolysaccharidosis (MPS I) IntroductionType I mucopolysaccharidosis (MPS I) is one of the most frequent lysosomal storage disorders (LSDs) and is due to the inherited deficiency of ␣-L-iduronidase (IDUA) activity, which results in the accumulation of its unprocessed substrates (glycosaminoglycans; GAGs) in many organs. 1 The disorder is systemic and clinically heterogeneous. Clinical manifestations include skeletal dysplasia, joint stiffness, visual and auditory defects, cardiac insufficiency, hepatosplenomegaly, and mental retardation. The clinical spectrum ranges from the severe Hurler syndrome (MPS I-H) to the attenuated Scheie syndrome. Mental retardation is distinctive only of MPS I-H, which is fatal in childhood if untreated, thus representing the variant with the most urgent need for new therapies. Enzyme replacement therapy (ie, parenteral administration of exogenous enzyme that can be internalized by tissue cells via the mannosium-6-phosphate receptor) is recommended only for MPS I patients without primary neurologic disease, due to the inability of the enzyme to efficiently cross the blood-brain barrier; moreover, neutralizing antibodies can attenuate its efficacy. 2 When performed at early ages, hematopoietic stem cell (HSC) transplantation (HCT) from healthy donors alleviates most disease manifestations in MPS I-H patients, likely by migration of the transplant-derived leukocytes into organs, where they can clear the storage and secrete the functional enzyme for correction of the metabolic defect in resident cells. 3 However, despite recent improvements in the outcome of HCT, the morbidity and mortality associated with the procedure are still not negligible, mostly due to rejection and graft-versus-host disease. Moreover, the amount of enzyme that transplantation can provide to the organism can be limiting, especially since donors are often heterozygous siblings. Indeed, a relationship between circulating enzyme levels after transplant and urinary GAGs has been shown 4 : the low enzyme levels achieved with heterozygote donor transplant lead to less adequate reduction in GAG levels. Likely due to partial metabolic correction at disease sites, the impact of HCT on central nervous system (CNS) and skeletal disease, despite being substantial in ameliorating patients' phenotype, could still benefit from further improvement. 5 The benefits of different gene therapy approaches were established in MPS I animal models. Intravenous delivery of viral vectors, which can establish a tissue source for systemic enzyme distribution, was effective in controlling disease manifestations in The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 USC section 1734. For personal use only. on May 10, 2018. by guest www.bloodjournal.org From MPS I animal models upon neonatal treatment. [6][7][8][9] However, residu...

Dogs with mucopolysaccharidosis VII (MPS VII)were injected intravenously at 2-3 days of age with a retroviral vector (RV) expressing canine ␤-glucuronidase (cGUSB). Five animals received RV alone, and two dogs received hepatocyte growth factor (HGF) before RV in an attempt to increase transduction efficiency. Transduced hepatocytes expanded clonally during normal liver growth and secreted enzyme with mannose 6-phosphate. Serum GUSB activity was stable for up to 14 months at normal levels for the RV-treated dogs, and for 17 months at 67-fold normal for the HGF͞RV-treated dog. GUSB activity in other organs was 1.5-60% of normal at 6 months for two RV-treated dogs, which was likely because of uptake of enzyme from blood by the mannose 6-phosphate receptor. The body weights of untreated MPS VII dogs are 50% of normal at 6 months. MPS VII dogs cannot walk or stand after 6 months, and progressively develop eye and heart disease. RV-and HGF͞RV-treated MPS VII dogs achieved 87% and 84% of normal body weight, respectively. Treated animals could run at all times of evaluation for 6 -17 months because of improvements in bone and joint abnormalities, and had little or no corneal clouding and no mitral valve thickening. Despite higher GUSB expression, the clinical improvements in the HGF͞RV-treated dog were similar to those in the RV-treated animals. This is the first successful application of gene therapy in preventing the clinical manifestations of a lysosomal storage disease in a large animal.