Significance of a new type of human fetal hemoglobin carrying a replacement isoleucine ? threonine at position 75 (E 19) of the ? chain

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Abstract
A new type of hemoglobin F, in which isoleucine in position 75 (E 19) of the γ chain is replaced by a threonine residue, has been found in 29 out of 32 homozygotes for β thalassemia. The amount of this hemoglobin ranges from traces to 40% of the total Hb F. The same γ75 Thr chain is also present in the Hb F of 40% of normal newborns and premature infants examined, of one 14-week-old fetus and in one out of 3 patients with aplastic anemia and raised levels of Hb F. Our results strongly suggest that the synthesis of this new chain is under the control of a γ gene nonallelic with those coding for Aγ and Gγ chains.