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Even though this is the best we can achieve at the moment, not all patients become free of transfusions and we still do not know the long-term effects of manipulating the genome of stem cells in this way, a major question hanging over this approach, which is hugely expensive, is whether this procedure, which involves killing off abnormal stem cells to replace them with modified stem cells, will ever become clinically possible in developing countries where the majority of these disorders of hemoglobin occur.