Identification of the Molecular Defect in the Erythrocyte Membrane Skeleton of Some Kindreds With Hereditary Spherocytosis

We have localized the molecular alteration in the membrane skeleton of two of four kindreds with hereditary spherocytosis (HS) to an alteration in the spectrin–protein-4.1 interaction due to a defective spectrin molecule. The defective spectrin–protein-4.1 interaction in these kindreds (referred to as type I HS) leads to a weakened spectrin–protein-4.1–actin ternary complex, which in turn may lead to the friable membrane skeleton and suggested membrane instability related to this disorder. Type I HS spectrin binds ~63% as much protein-4.1 as normal spectrin (with equal affinity). This defect does not correlate with splenic function or erythrocyte age in the circulation. However, the ~37% reduction in binding of protein-4.1 to HS spectrin approaches the theoretical value of 50% expected in this autosomal dominant disorder. All other type I membrane skeletal interactions (spectrin–syndein, spectrin heterodimer–heterodimer, syndein–band-3) were found to be normal. It would appear therefore that the defective HS spectrin–protein-4.1 interaction in type I hereditary spherocytosis may be the primary molecular defect rather than a secondary phenomena.