Hemoglobin Bart's Levels in Umbilical Cord Blood: Failure as a Method for Distinguishing Mild from Severe α-Thalassemia Trait in the Chinese

Abstract

α-Thalassemia is associated with a defect in the production of the α-globin chains of hemoglobin. There are four common varieties in decreasing order of severity: the hemoglobin (Hb) Bart's (γ₄) hydrops fetalis syndrome, hemoglobin H disease, “severe” heterozygous α-thalassemia or α-thal-1 trait and “mild” heterozygous α-thalassemia or α-thal-2 trait (1) and there is now evidence that these may be the result of deletion of 4, 3, 2, and 1 respectively of the α-globin structural genes (2, 3, 4). As a result of defective α-globin chain production, the umbilical cord blood of infants with Hb Bart's hydrops fetalis contains from 80 to 90 per cent Hb Bart's (1) and those with Hb H disease, about 26 per cent (5). In newborn infants with α-thalassemia trait, lesser amounts of Hb Bart's have been found (5, 6, 7, 8). Observations in Thailand suggest that they fall into two groups, those with about 5 per cent Hb Bart's and others with from 1-2 per cent (9). The former were designated to have α-thal-1 trait and the latter the α-thal-2 trait. However, there is uncertainty as to whether a clear-cut division between these two groups of infants can be made on this basis (1) and in the present study we have been unable to find a bi-modal distribution of Hb Bart's levels in the cord blood of Chinese infants with α-thalassemia trait.