Three generations of a Negro family having herditary persistence of fetal hemoglobin in conjunction with the hemoglobins A and S were studied.

Genetic studies did not exclude the possibility that this anomaly is allelic with the genes responsible for the hemoglobins A, S, and C.

Structural investigations of the isolated abnormal hemoglobin fraction offered evidence that this component is identical with the fetal hemoglobin of the newborn child.

No striking clinical or hematologic abnormalities were found in members of the family who had high percentages of fetal hemoglobin in conjunction with either Hb-A or Hb-S. The per cent of Hb-A2 in the persistent high Hb-F carriers was found slightly below normal, while the total amount of circulating hemoglobins was increased. Previous reports of the complete absence of Hb-A in cases heterozygous for Hb-S as well as for the persistent high Hb-F anomaly have been confirmed by using refined technics available for hemoglobin analyses.

The fetal hemoglobin was distributed almost equally in all erythrocytes of individuals having this inherited anomaly. In this respect, the S-F abnormality differs from homozygous sickle-cell disease in which a mixed population of red blood cells, some with and most without Hb-F, has been demonstrated. It is suggested that the presence of some Hb-F in all erythrocytes of the individual with the S-F condition is the factor that protects the cells from sickling and from destruction.

The distribution of fetal hemoglobin in the red blood cells of persistent high Hb-F carriers was also different from that found in patients with thalassemia major and thalassemia-Hb-E disease. Two distinct cell populations, one with and the other without fetal hemoglobin, were found to be present in the blood of the thalessemia patients.

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