Positional effect of cis/trans alpha globin gene deletions on the formation of “H” bodies
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abstract
AbstractNormal individuals have four AaL‐globin genes, two on each member of the chromosome 16 pair (αα/αα). The α‐thalassemia trait phenotype associated with deletions of two α‐genes can be either on the same chromosome, the cis type (αα/—), or on opposite chromosomes, the trans type (α‐/α‐). Traditionally, the observation on vitally stained smears of occasional cells containing “H” bodies has been used as an important diagnostic criterion for α‐thalassemia trait. These “H” bodies are thought to be precipitated β tetramers because of the presence of excess β‐globin chains. Our study in patients with various α‐genotypes indicates that normal subjects (αα/αα) and patients with silent α‐thalassemia trait (αα/α‐) generally have no “H” bodies. However, patients with the two‐gene deletion of the cis type α‐thalassemia (αα/—) show the occasional “H” body, and those with Hb “H” disease (α‐/—or αcs‐/—) show many such bodies. On the other hand, patients with two‐gene deletion of the trans type (α‐/α‐) do not show “H” bodies.The number of “H” bodies found does not appear to correlate directly with the degree of imbalance in α‐ and β‐chain production among the various α‐genotypes examined. The chemical nature of “H” bodies is discussed, and an alternative hypothesis that embryonic ζ chains expressed in the cis type but not in the trans type of α‐thalassemia are involved in the formation of “H” bodies is proposed.
