POINT MUTATION IN THE BETA-SPECTRIN GENE ASSOCIATED WITH ALPHA-I/74 HEREDITARY ELLIPTOCYTOSIS - IMPLICATIONS FOR THE MECHANISM OF SPECTRIN DIMER SELF-ASSOCIATION

αI/74 hereditary elliptocytosis (HE) is a subgroup of HE in which patients exhibit an impaired self-association of spectrin dimers and an abnormal proteolytic cleavage of the αI domain of spectrin. We studied a family in which the proband presented with a severe neonatal hemolytic anemia with poikilocytosis. Biochemical analysis of erythrocytes from the proband and his family members allowed us to ascertain a diagnosis of homozygosity for αI/74 HE in the proband and heterozygosity in his parents and several of their offspring. Results of polymorphism linkage analysis suggested that the defect in this family was located in β rather than α spectrin. We analyzed the 3′ end of the β-spectrin gene of the proband and detected a mutation that changes a codon for alanine to one for proline. Allele-specific oligomer hybridization on slot blots of DNA from other family members confirmed the presence of the mutation only in members heterozygous for the disorder. This is the first example of a point mutation in the β-spectrin chain that is associated with defective spectrin dimer self-association and an abnormal proteolytic cleavage of the α chain. Based on this finding, we propose a model for the mechanism of interaction between the α- and β-spectrin chains.