Hb Amsterdam-A1 [α32(B13)Met→Ile; HBA1: c.99G>A]: A Hyperunstable Variant Due to a New Mutation on the α1 Gene.

Patients with hyperunstable α chain variants usually present with a thalassemic, rather than hemolytic, phenotype. Electrophoretic, ion exchange and reverse phase separations usually fail to detect the variant and when DNA sequencing identifies a 'silent' substitution it is usually presumed to be hyperunstable. We report the identification of such a variant, α32(B13)Met→Ile; HBA1: c.99G>A, arising from a new mutation on the α1 gene. The hemoglobin (Hb) was unequivocally detected by the isopropanol stability test and confirmed as hyperunstable by mass spectrometry (MS) of the precipitate and lysate, which showed proportions of 55% and 2.5% of α chains, respectively. The instability appears to be driven by perturbation of globin-heme, and possibly α1β1 subunit, interactions.