Laboratory recognition of a rare hemoglobinopathy: hemoglobins SS and SG(Philadelphia) associated with alpha-thalassemia-2.

Abstract

This article describes the laboratory investigation of an unusual hemoglobinopathy involving hemoglobin (Hb) S, HbSG(Philadelphia), and alpha-thalassemia-2 in a patient whose phenotype was HbSC by alkaline electrophoresis. Findings of a mean corpuscular volume of 62 fL and microcytes on the blood smear were inconsistent with HbSC disease. The patient's clinical course over several years had been mildly symptomatic. Testing in our hospital laboratory using isoelectric focusing and cation-exchange high-performance liquid chromatography to separate hemoglobins showed an unknown variant. Additional studies, including globin chain electrophoresis, reverse-phase high-performance liquid chromatography, and polymerase chain reaction-based DNA analysis were performed at reference laboratories, which reported the following findings: HbG(Philadelphia) associated with alpha-thalassemia-2, HbS and HbG(Philadelphia), and the alpha-globin deletions defining the -alpha3.7/-alpha3.7 genotype. The hemoglobin molecular defects, alpha-thalassemia-2, and the pattern of inheritance are discussed.