Significance of a new type of human fetal hemoglobin carrying a replacement isoleucine replaced by threonine at position 75 )E 19) of the gamma chain.

A new type of hemoglobin F, in which isoleucine in position 75 (E 19) of the gamma chain is replaced by a threonine residue, has been found in 29 out of 32 homozygotes for beta thalassemia. The amount of this hemoglobin ranges from traces to 40% of the total Hb F. The same gamma75 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 gamma gene nonallelic with those coding for Agamma and Ggamma chains.