Hereditary spherocytosis with spectrin deficiency due to an unstable truncated beta spectrin

Abstract

Red cell membrane protein analysis by sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE) and direct quantitation by radioimmunoassay or cytofluorometry defines four distinct subsets of patients with hereditary spherocytosis: Patients with isolated spectrin deficiency, combined spectrin and ankyrin deficiency, band 3 deficiency, and protein 4.2 deficiency. In regard to the first group, only one mutation of beta spectrin has been reported in the literature. We describe a spectrin variant characterized by a truncated beta chain, and associated with hereditary spherocytosis and isolated spectrin deficiency. The clinical phenotype consists of a moderate hemolytic anemia with spherocytosis and frequent spiculation of the red cells. We present the biochemical characteristics of this mutant protein and show that it constitutes only 12% of the total spectrin on the membrane. We show that the truncation of the protein is the result of a single point mutation at position +1 (G-->A) of the donor consensus splice site of intron 17 leading to an aberrant beta spectrin transcriptional message lacking exons 16 and 17. To elucidate the basis for the decreased amount of the truncated protein on the membrane and the overall spectrin deficiency, we provide evidence that the mutated gene is transcribed but its mRNA is less abundant than its normal counterpart in reticulocytes; we also show that the mutant protein is synthesized in decreased amounts in the cytoplasm of erythroid progenitor cells, and appears to be susceptible to proteolytic degradation. This mutant spectrin underscores the importance of the regulatory role played by the beta spectrin molecule in the assembly of alphabeta spectrin heterodimers on the membrane.

Mutational characteristics of ANK1 and SPTB genes in hereditary spherocytosis

“…In this study, four patients from two families with non-HS showed mutations in spectrin tetramer (SPTA1 p.Arg41Trp and SPTB p.Phe2014Val) and homozygous SPTB mutation revealed HPP whereas heterozygous SPTA1 one revealed HE. Several patients harboring SPTB mutations on domain outside of tetramer were initially misreported as HS and self-corrected as HE by the researchers (42,43). A comprehensive literature review reinforced the finding that mutations in spectrin tetramer are associated with HE or HPP and mutant dosage (heterozygous and homozygous) affects the disease phenotype.…”

Novel beta‐spectrin mutations in hereditary spherocytosis associated with decreased levels of mRNA

“…Relative mRNA quantification of red cell membrane protein genes in Polish patients indicated that SPTB could be involved in anaemia pathogenesis. Most of the SPTB gene defects identified so far are splicing, frameshift and nonsense mutations that lead to transcript instability or truncation of the spectrin β protein (Dhermy et al , 1998; Hassoun et al , 1996, 1997). With the exception of some polymorphic amino acid changes, no common mutation has been described.…”

“…To date, several mutations in SPTB have been discovered and their effects studied in detail (Gallagher & Forget, 1998). These include various missense, as well as splicing, frameshift and nonsense mutations, that usually result in mRNA processing defects and truncated spectrin β variants (Dhermy et al , 1998; Hassoun et al , 1996, 1997). The currently known HS‐associated SPTB changes are scattered all over the SPTB gene, which is over 100 kb in length and consists of 32 exons (Iolascon et al , 1998; Maillet et al , 1996).…”

β‐Spectrin Sta Bárbara: a novel frameshift mutation in hereditary spherocytosis associated with detectable levels of mRNA and a germ cell line mosaicism

“…Deficiency of protein 4·2 has been reported, but it is less common in western populations (Gallagher et al , 1998). β‐spectrin‐related HS is relatively common (Becker et al , 1993; Hassoun et al , 1995, 1996, 1997; Garbarz et al , 1998; Bassères et al , 1998; Dhermy et al , 1998), and is frequently a result of null mutations, in which the mutant mRNA is unstable and the allele is not expressed (Hassoun et al , 1997; Dhermy et al , 1998; Miraglia del Giudice et al , 1998). One other characteristic feature of β‐spectrin‐related dominant HS is the presence of acanthocytes in the blood smear (Hassoun et al , 1997).…”