Summary: 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 [alpha]-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 [beta]/[alpha] ratio was observed in the first group; microcytosis and hypochromia were absent in the children of the second group although the [beta]/[alpha] ratio was significantly increased. The [alpha] chain deficiency is familial. Increased [alpha]/[alpha] 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.
Speculation: It is postulated that the absence or presence of duplicated Hb[alpha] structural genes is the underlying mechanism for the variable [alpha] chain deficiency in black infants. Children with about 5% Hb Bart's at birth have the genotype -[alpha]/- [alpha] or, rarely, the -/[alpha] [alpha] genotype; when only two Hb[alpha] structural loci instead of four are active, a modest deficiency in a chain production will be the result. The presence of the -[alpha]/[alpha][alpha] 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 -[alpha]/[alpha] genotype however, is also suggested from data obtained by MCH and MCV determinations. It is concluded that although the -[alpha]/[alpha] genotype always produces Hb Bart's at birth in moderate amounts, the -[alpha]/[alpha][alpha] genotype may or may not. The rarity of the - -/[alpha][alpha] genotype in this population is responsible for the absence of the Hb Bart's hydrops fetalis syndrome.
(C) International Pediatrics Research Foundation, Inc. 1977. All Rights Reserved.