Sir.—In the July issue of the Journal (128:18, 1974), Karp et al demonstrated a 5.5% incidence of microcytic anemia in predominantly black, 5-through 8-year-old inner-city children. The authors suggest that nutritional iron deficiency, rather than an inherited condition such as a thalassemia trait, is the cause of these microcytic red blood cell indexes. They base this assumption on "... the association of sociological characteristics [and the] fact that ferrous sulfate treatment of a representative subpopulation of the study group produced a significant rise in MCV...."
Two recent studies of over 900 black Americans reported incidence of α thalassemia trait in 2% to 3% of this population.1,2 The incidence of high-A2 β thalassemia in black Americans is reported to be 1%.3 The authors report finding only one of 1,210 children tested who had microcythemia and an elevated hemoglobin A2 level. The extremely low incidence of high-A