IntroductionBone marrow transplantation (BMT) is an established therapeutic modality for both malignant and nonmalignant disorders of hematopoietic stem cells. After wide recognition that bone marrow also contains progenitors of bone, [1][2][3][4] we postulated that BMT should be applicable to the treatment of osteopoietic as well as hematopoietic disorders. 5 Nilsson et al demonstrated that transplantation of whole bone marrow leads to donor-derived osteopoiesis in mice, 6 while Pereira et al showed that systemically infused murine mesenchymal stromal cells (MSCs), which are plastic adherent in vitro, 7 engrafted in bone. 3 We showed that BMT in children with osteogenesis imperfecta (OI), a genetic disorder of collagen type I, the major structural protein in bone, leads to donor-derived osteopoiesis and consequent improvement in the microscopic structure of bone 5 and in the clinical manifestations of OI. 8 Recently, BMT in a murine model of OI has corroborated our early human studies. 9 Taken together, these data validate the functional competence of donor-derived osteopoietic cells, providing the necessary proof to move forward with the development of marrow cell-based treatments for disorders of bone.Despite this progress, the cellular mechanism(s) by which BMT gives rise to robust osteopoietic activity remains unproven. Pereira et al reported that systemically infused murine MSCs engrafted in the bone of a murine model of OI, and generated a small but statistically significant increase in collagen, 10 supporting the prevailing view that BMT-associated donor-derived osteopoiesis was attributable to the engraftment and differentiation of MSCs. Thus, we reasoned that a decrease in the rate of clinical improvement in our OI patients after BMT 8 might be corrected with a boost of donor-derived MSCs, which in fact led to a second wave of accelerated growth velocity in all 5 evaluable patients. 11 This result suggested that MSCs isolated on the basis of their adherence to plastic may provide adequate therapy for patients with OI or other bone disorders. However, the issue is complicated by work showing that so-called nonadherent bone marrow cells (NABMCs) have measurable osteoprogenitor activity, 12-14 raising questions as to the developmental origin of the transplantable marrow osteoprogenitors that give rise to donor-derived osteopoiesis and hence to the marrow population most likely to yield clinical improvement in patients.Here we show that NABMCs are significantly more robust transplantable osteoprogenitors than MSCs in mice, suggesting NABMC would be effective cell therapy for bone disorders. Translating this laboratory observation to a pilot clinical trial, T cell-depleted marrow mononuclear cells, comprising Ͻ 0.01% MSCs, engraft in bone after intravenous infusion and lead to a remarkable acceleration of growth in some OI patients, suggesting vigorous osteoprogenitor activity in humans as predicted by our animal model. Finally, we demonstrate that NABMCs produce their clinical activity by engrafting in bon...

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Short chain acyl-CoA dehydrogenase deficiency (SCADD) is a disorder of mitochondrial fatty acid oxidation that leads to the accumulation of butyrylcarnitine and ethylmalonic acid in blood and urine. Originally described with a relatively severe phenotype, most patients are now diagnosed through newborn screening by tandem mass spectrometry and remain asymptomatic. Molecular analysis of affected individuals has identified a preponderance of private inactivating point mutations and one common one present in high frequency in individuals of Ashkenazi Jewish ancestry. In addition, two polymorphic variants have been identified that have little affect on enzyme kinetics but impair folding and stability. Individuals homozygous for one of these variants or compound heterozygous for one of each often show an increased level of ethylmalonic acid excretion that appears not to be clinically significant. The combination of asymptomatic affected newborns and the frequent variants can cause much confusion in evaluating and treating individuals with SCADD. The long term consequences and the need for chronic therapy remain current topics of contention and investigation.