Homozygous State for Hb Constant Spring (Slow-moving Hb X Components)

A 12-yr-old Malay boy who was studied because his youngest brother and both his parents had the slow-moving Hb X components (earlier reported to lead to Hb H disease when combined with α-thalassemia) was found to be homozygous for the same slow-moving components. He had splenomegaly and a just palpable liver, mild anemia with microcytosis, hypochromia, slight morphologic changes of the red blood cells, and slight reticulocytosis. Of eight children in the family, six had the trait for the abnormality, one was normal, and one, the propositus, was homozygous. Structural studies of the isolated abnormal hemoglobin showed it to be identical to Hb Constant Spring (Hb CoSp), an α-chain variant with 172 residues instead of the usual 141, the additional 31 being attached to the C-terminal end. In addition to the abnormal α variant for which the propositus was homozygous, he also had normal Hb A and normal Hb A₂ with normal α-chains. If the theory that Hb CoSp is due to a structural mutation affecting the terminator codon is correct, this case provides evidence for a duplication of the gene for α-chain production. Results of study of several erythrocyte enzymes are also reported.