Hematologists know only too well that anemia is not a diagnosis but is the recognition of a sign for which we must find the cause and work out the pathogenetic mechanism, which ultimately must be explainable at the molecular level. Overall, for the majority of acquired anemias, things are by now pretty clear with respect to etiology but not necessarily with respect to molecular mechanisms. For instance, although we do understand that iron deficiency limits heme synthesis and consequently hemoglobin synthesis, we do not know exactly how the mean cell volume (MCV) is controlled by the supply of iron: for this reason we have omitted from this chapter a section on the commonest anemia of all—iron deficiency anemia. However, it is gratifying that we can at least offer a model for the molecular basis of megaloblastic anemia, another major public health problem in many countries. With respect to the majority of congenital anemias, and certainly for the commonest among them, molecular genetics has answered not all, but most of the questions with respect to etiology and pathogenesis.
However, lest we become complacent, we must admit that, as is often the case in medicine, the time lag between fundamental discoveries and therapeutic applications too often remains too long, and that advances in knowledge are not always used wisely. On the one hand, we saw recently a patient with PNH who had massive hemoglobinuria and had become severely iron-deficient as a result. He had been treated with erythropoietin, but not with iron: a few weeks of 400 mg of ferrous sulfate daily raised his hemoglobin level from 6.7 to 10.1 g/dl. On the other hand, for patients who have, for instance, severe chronic hemolytic disease due to PK deficiency, the outlook has improved only because we can offer better supportive treatment—not because we know the molecular basis. The latter will only become relevant once we learn to correct the PK deficiency by gene addition or by gene replacement. This is a major and worthy challenge for the next decade with respect to all the genetically determined anemias.
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