Hemoglobin ? chain deficiency in black children with variable quantities of hemoglobin Bart's at birth

Abstract

Hematologic and globin chain synthesis studies have been made in 21 children, aged 2 to 6 years, many of their parents, and several normal adults and ?-thalassemia heterozygotes. At birth, 11 children had about 5% hemoglobin (Hb) Bart's, 5 had about 2% Hb Bart's, and 5 had no trace of Hb Bart's. A significant decrease in mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) values and an increase in the ?/? ratio was observed in the first group; microcytosis and hypochromia were absent in the children of the second group although the ?/? ratio was significantly increased. The ? chain deficiency is familial. Increased ?/? ratios were present in many parents although only two parents of children with 5% Hb Bart's at birth had hematologic findings suggestive of the presence of the same type of defect as observed in the children with the larger amount of Hb Bart's at birth. It is postulated that the absence or presence of duplicated Hb(?) structural genes is the underlying mechanism for the variable ? chain deficiency in black infants. Children with about 5% Hb Bart's at birth have the genotype -?/-? or, rarely, the --/?? genotype; when only two Hb(?) structural loci instead of four are active, a modest deficiency in ? chain production will be the result. The presence of the -?/?? genotype could be predicted from the small amounts of Hb Bart's at birth and from data of the hemoglobin synthesis analyses in older children and adults; the -?/? genotype however, is also suggested from data obtained by MCH and MCV determinations. It is concluded that although the -?/? genotype always produces Hb Bart's at birth in moderate amounts, the -?/?? genotype may or may not. The rarity of the --/?? genotype in this population is responsible for the absence of the Hb Bart's hydrops fetalis syndrome. � 2017 Elsevier B.V., All rights reserved.