Hb Sun Prae or α₂13o(H13)Ala → Proβ₂ A New Unstable Variant Occurring In Low Quantities

Abstract

A severe hemolytic anemia with microcytosis and hypochromia was present in a young adopted Indian patient. Reversed phase high performance liquid chromatographic methodology and heat stability tests detected an unstable α chain which was present in 3 to 5% of the total hemoglobin. A larger quantity of the α^x chain was obtained by preparative reversed phase high performance liquid chromatography. Structural analyses identified an Ala → Pro replacement at position 130 of the a chain. The instability of the variant, named Hb Sun Prairie, is comparable to that of Hb Bibba [αl36 (H19)Leu → Pro]. Gene mapping failed to detect an α-thalassemia deletion (αα/αα), while dot-blot analysis of amplified DNA with synthetic probes localized a G → C mutation in codon 130 (resulting in the Ala → Pro mutation) of the α2-globin genes of both chromosomes. These results suggest a homozygosity for the G → C mutation and the condition α2(G → C)αl/α2(G → C)αl adequately explains the rather severe clinical status of this child, including the marked microcytosis and hypochromia. Unfortunately, family studies to exclude the presence of a large deletion involving all ζ- and α-globin genes were not possible.