Heterogenous band 3 deficiency in hereditary spherocytosis related to different band 3 gene defects

Among 80 hereditary spherocytosis (HS) kindreds studied using denaturing electrophoretic separation of solubilized eythrocyte membrane proteins, we recognized three prominent subsets: HS with isolated spectrin deficiency, HS with combined spectrin and ankyrin deficiency, and HS with band 3 deficiency. These three subsets represent more than 80% of the HS kindreds studied. In this study, eight dominant HS kindreds with band 3 deficiency were investigated for band 3 mutations. In three of these kindreds, linkage analyses confirmed the band 3 gene as the culprit gene. In an attempt to identify the responsible mutations, denaturing gradient gel electrophoresis (DGGE) was used to explore the coding exons (exons 2-20) of band 3 gene. Five different mutations were found in the eight kindreds. In five kindreds we identified substitutions of highly conserved residues, positioned at boundaries of putative transmembrane segments: C --> T substitution at codon 490 changed arginine ((C) under bar GC) to cysteine ((T) under bar GC) in three kindreds, a C --> T substitution at colon 837 changed threonine (A (C) under bar G) to methionine (A (T) under bar G) in two kindreds. In the sixth kindred a G deletion was found in a stretch of five G starting at position 1475, leading to a stop codon either at position 1527 or 1565. In the seventh kindred a T deletion at position 1600 resulted in a stop codon at position 1733 and in the last kindred a T deletion was identified at position 355, leading to a stop codon at position 447. The mutant transcript was present in HS patients bearing missense mutations, whereas only the normal transcript was found in HS patients with frameshift mutations. In the latter group the mean decrease in membrane band 3 content was significantly lower, leading to speculation that missense mutations may have some sort of dominant negative effect.