Novel exon 2 α spectrin mutation and intragenic crossover: three morphological phenotypes associated with four distinct α spectrin defects

Abstract

Hereditary pyropoikilocytosis is a severe hemolytic anemia caused by spectrin deficiency and defective spectrin dimer self-association, typically found in African populations. We describe two Utah families of northern European ancestry including 2 propositi with atypical non-microcytic hereditary pyropoikilocytosis, 7 hereditary elliptocytosis members and one asymptomatic carrier. The underlying molecular defect is a novel mutation in the alpha(α) spectrin gene, SPTAR34P that impairs spectrin tetramer formation. It is inherited in trans to the hypomorphic SPTAαLELY in the 2 propositi and 5 of 7 hereditary elliptocytosis individuals indicating that SPTAαLELY is not the sole determinant of the variable clinical expression. α Spectrin mRNA was mildly decreased in all hereditary elliptocytosis subjects, whereas both hereditary pyropoikilocytosis propositi had a severe decrease to ~10% of normal. Genotyping identified a unique SPTA intragenic crossover and uniparental disomy in one hereditary elliptocytosis individual. Two additional crossover events demonstrated the susceptibility of SPTA gene to rearrangement and revealed a novel segregation of the two SPTAαLELY mutations. We conclude that the profound phenotypic heterogeneity in these families can be attributed to the SPTAR34P mutation in combination with: 1) inheritance in trans of either SPTAαLELY; or 2) the wild-type SPTA; 3) a decrease of α spectrin mRNA; and 4) SPTA intragenic crossover.