Hb Amsterdam [α32(B13)met→ile (α2)]: A new unstable variant associated with an α-thalassemia phenotype and a new African polymorphism

□ We have characterized a new abnormal hemoglobin (Hb) at position 32 of the α-globin chain. The proband, a 38-year-old woman of Surinamese Black ancestry, was referred to the Academic Hospital in Amsterdam, The Netherlands, after 3 years of Prednisone treatment in Surinam. Kidney failure was diagnosed at the Nephrology Department, Free University Medical Center, Amsterdam, The Netherlands; the cortisone treatment was interrupted and dialysis was started. At this stage, a microcytic hypochromic anemia was observed with high reticulocyte (40%) and ferritin (500 μg/L) levels, and hemoglobinopathy was suspected. No abnormal bands were visible on alkaline electrophoresis and high performance liquid chromatography (HPLC). The Hb A₂ level was normal (2.7%) and the erythrocyte count was low (3.59 × 10¹²/L) with a normal haptoglobin level (68 mg/100 mL). None of the common α-thalassemia (thal) deletion defects were present. The β-globin gene sequence was normal but the α2-globin gene sequence revealed an ATG→ATA transition at codon 32, changing the methionine into an isoleucine residue. The mutation, called Hb Amsterdam, was observed in the mother of the proband, who was also heterozygous for the -α^3.7-thal deletion and affected by a moderate microcytic hypochromic anemia. Both Hb Amsterdam and the -α^-3.7 allele were found in association with a new polymorphism, IVS-I-39 (C→T), previously observed in our laboratory in seven patients of African origin, on both the α1 and α2 genes. In addition, Hb Amsterdam was also associated with the common African α2 polymorphism (G→CTCGGCCC at position 7238 and T→G at position 7174). Hb Amsterdam is the first mutation ever described at codon α32, a position involved in α1/β1 interaction. The possibility of a contribution of this mutation to the nephropatic state of the proband is discussed.