Aberrant splicing contributes to severe α-spectrin-linked congenital hemolytic anemia

The etiology of severe hemolytic anemia in most patients with recessive hereditary spherocytosis (rHS) and the related disorder hereditary pyropoikilocytosis (HPP) is unknown. Whole-exome sequencing of DNA from probands of 24 rHS or HPP kindreds identified numerous mutations in erythrocyte membrane a-spectrin (SPTA1). Twenty-eight mutations were novel, with null alleles frequently found in trans to missense mutations. No mutations were identified in a third of SPTA1 alleles (17/48). WGS revealed linkage disequilibrium between the common rHS-linked alpha(BH) polymorphism and a rare intron 30 variant in all 17 mutation-negative alleles. In vitro minigene studies and in vivo splicing analyses revealed the intron 30 variant changes a weak alternate branch point (BP) to a strong BP. This change leads to increased utilization of an alternate 3' splice acceptor site, perturbing normal alpha-spectrin mRNA splicing and creating an elongated mRNA transcript. In vivo mRNA stability studies revealed the newly created termination codon in the elongated transcript activates nonsense-mediated decay leading to spectrin deficiency. These results demonstrate that a unique mechanism of human genetic disease contributes to the etiology of a third of rHS cases, facilitating diagnosis and treatment of severe anemia and identifying a new target for therapeutic manipulation.