(1) Four Negro patients with mild sickle cell-thalassemia disease (heterozygous for the genes for S hemoglobin and for thalassemia) are described. In contrast to reports in the literature, some of these patients are only mildly anemic, or not anemic at all. In three, the values for MCV and MCH are decreased, but in one, all hematologic indices are normal. All four individuals show leptocytosis and elevated reticulocyte levels.

(2) Hemoglobin analyses, consisting of a combination of electrophoresis and the alkali denaturation technic, demonstrate the S + A + F pattern in three, and the S + A pattern in the fourth. These patterns are considered pathognomonic for sickle cell-thalassemia disease. They may be sharply differentiated from the S + F pattern, encountered in classical (homozygous) sickle cell anemia, and from the A + S pattern found in the heterozygous sickle cell trait. The various types of hemoglobin are reported in the sequence of their quantitative representation in the hemolysate. Hemoglobin analysis is indispensable for the recognition of the different types of sickle cell disease.

(3) Evidence is cited that clinically almost asymptomatic sickle cell-thalassemia disease is probably not too rare in the American Negro population.

(4) The genetic aspects of the production of fetal hemoglobin are discussed. It is postulated that the production of fetal hemoglobin is also under genetic control. The genes for fetal hemoglobin are not alleles of the genes for normal adult hemoglobin and are physiologically almost completely suppressed by the latter. Pathologic genes may render this suppression incomplete.

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