Severe recessive poikilocytic anaemia with a new spectrin α chain variant

Abstract

A severe neonatal haemolytic anaemia was observed in a propositus from the West Indies. Frequent blood transfusions were required until complete splenectomy was carried out. Blood smears showed predominant poikilocytosis with spherocytes and microcytes as observed in hereditary pyropoikilocytosis. Erythrocytes were completely fragmented after incubation at 45 degrees C. The two asymptomatic parents had normal haematological profiles. The erythrocyte membrane electrophoretic patterns of the splenectomized propositus and her parents were normal. The propositus had a moderate defect in the spectrin (Sp) dimer self-association. Limited tryptic digestion of the propositus' Sp under standard conditions (0 degrees C, 20 h, enzyme-substrate ratio of 1/100) revealed an increased sensitivity to tryptic digestion. The major features detected by one- and two-dimensional electrophoresis gels of Sp tryptic digests were the absence of high molecular weight peptides from the Sp alpha II (48 kDa and 35 kDa peptides) and Sp alpha III (52 kDa peptide) domains with increased amounts of the lower molecular weight peptides from the Sp alpha II and Sp alpha III (29 kDa peptide and 47 kDa peptide) domains respectively. Kinetic studies of Sp tryptic digestion (10 min to 36 h) confirmed the increased tryptic susceptibility of Sp. Immunodetection with specific anti-alpha-chain domain antibodies showed that the highest molecular weight peptides from the alpha II and alpha III domains are released early in digestion, but disappear quickly, with an increase in their corresponding smaller peptides. The molecular weights of the peptides corresponding to the 48 kDa and 35 kDa peptides from the alpha II domain are slightly modified. Peptides from the alpha I and alpha IV domains showed no significant abnormalities. The Sps of both parents were normal. These results indicate that the patient has a novel Sp alpha chain defect, which is probably located in the region of the alpha II domain which adjoins the alpha III domain.