LOW EXPRESSION ALLELE-ALPHA(LELY) OF RED-CELL SPECTRIN IS ASSOCIATED WITH MUTATIONS IN EXON-40 (ALPHA(V/41)-POLYMORPHISM) AND INTRON-45 AND WITH PARTIAL SKIPPING OF EXON-46

The alpha(v/41) polymorphism of erythroid alpha-spectrin has been characterized initially by an increased susceptibility to proteolysis of the alphaIV-alphaV domain junction (Alloisio N., L. Morle, J. Marechal, A.-F. Roux, M.-T. Ducluzeau, D. Guetarni, B. Pothier, F. Baklouti, A. Ghanem, R. Kastally, et al. 1991. J. Clin. Invest. 87:2169-2177). Until now, it has been found associated invariably with a low expression level of the corresponding a chain. Among 61 chromosomes investigated in French and North African individuals or kindreds, we observed 19 chromosomes with the alpha(v/41) polymorphism. With no single exception, the latter displayed a point mutation in exon 40 (Leu --> Val; CTA --> GTA) at position alpha 1857. According to the triple helical model of spectrin structure, this change accounts for the peptide maps' abnormalities. Sequencing the entire alphaV domain cDNA disclosed, in addition, a partial skipping of exon 46. At the gene level, a substitution (C --> T) was evidenced at nucleotide -12 of intron 45. This mutation appeared linked to the exon 40 mutation in 17 chromosomes, again with no single exception, among 53 examined chromosomes. We hypothesized that the lack of exon 46 would hamper the nucleation process and eventually account for the low expression feature. The present doubly mutated allele was renamed allele alpha(LELY) (low expression, Lyon).