Background. Mucopolysaccharidosis type VI (MPS VI) is the lysosomal storage disorder caused by the deficient activity of arylsulfatase B (ASB). In this study, we evaluated bone marrow transplantation (BMT) for the treatment of MPS VI and the effects of irradiation on the survival and engraftment of bone marrow-transplanted neonatal rats. Methods. One- to 2- day-old MPS VI rats were injected with normal bone marrow after irradiation with 200, 400, or 800 cGy. Ninety percent of the animals receiving a single dose of 200 cGy (n=30) survived the procedure, whereas irradiation with 400 cGy (n=23) or 800 cGy (n=12) resulted in significant mortality (78% and 100%, respectively). Engraftment was monitored by determining ASB activities in peripheral white blood cells and by Y chromosome in situ hybridization analysis. Fifty-two percent of the animals from the 200-cGy group engrafted for up to 8 months after BMT; among the five animals that survived the 400- cGy dose, all engrafted. In comparison, only 20% of nonirradiated animals engrafted at low levels. Of the 24 engrafted animals that were monitored for 8 months after BMT, clinical and/or radiographic improvements were noted in only one (BMT animal 3). Enzymatic analysis revealed that the ASB activities in the reticuloendothelial organs of this animal, as well as two other engrafted but clinically unimproved animals (BMT animals 1 and 2), were normal or near normal; correspondingly, the glycosaminoglycan levels in these organs were significantly reduced. Consistent with the clinical and biochemical observations, light and electron microscopic findings were more improved in BMT animal 3 as compared with BMT animals 1 and 2, although a reduction of storage was evident in each of these transplant recipients, particularly in the trachea and aorta, two tissues that are characteristic sites of pathology in human patients. Conclusions. These results indicate that BMT in newborn MPS VI patients may prevent many of the pathological and clinical findings in this disorder, but is likely to have very limited and unpredictable effects on the skeletal abnormalities.
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