Coinheritance of two α-spectrin gene defects in a recessive spherocytosis family

Abstract

We studied a recessive hereditary spherocytosis (HS) family from Norway in which all four children had haemolytic spherocytosis while spectrin (Sp) deficiency was detected in the proband. Molecular analysis demonstrated that all affected children had inherited the low expression alpha-Sp allele LEPRA (Low Expressed PRAgue) from the father. Haplotyping with a polymorphic dinucleotide repeat for the alpha-Sp gene (alphaVNTR) located in the 3' untranslated region of mRNA showed that all recessive children had inherited the same maternal alpha-spectrin allele. The paternal Sp-alphaLEPRA allele was found in cis of the polymorphic alpha-Sp Bughill allele (alphaBH) characterized by the A970D point mutation in the Sp alpha-chain. This mutation was identified on two-dimensional electrophoresis of Sp tryptic digests as an acidic shift of the alphaII tryptic domains (spots alphaIIa). Analyses of the relative expression of the paternal alpha-Sp Bughill polymorphism in the proband showed that the product of the maternal alpha-Sp gene is almost completely absent from the mature erythrocyte membrane. Comparative analysis between alphaVNTR PCR-amplified from genomic DNA and from cDNA showed that the maternal low expression alpha-Sp allele is associated with a decreased amount of mRNA. Results from molecular and biochemical studies showed that all the affected children of this family are compound heterozygous for two different low expression alpha-Sp alleles: an uncharacterized defective alpha-Sp allele on the maternal side and an alphaLEPRA allele tagged by the alphaIIa polymorphism on the paternal side.

ICSH guidelines for the laboratory diagnosis of nonimmune hereditary red cell membrane disorders

“…Finally, α spectrin alleles in patients with isolated spectrin deficiency and a co‐inheritance of defective β spectrin gene have to be investigated at the molecular level to distinguish between a mutation or a polymorphic allele (e.g. spectrin α LEPRA ) responsible for the recessive pattern of inheritance .…”

“…A higher incidence of partial spectrin deficiency is associated with moderate and severe HS. Since only a handful of pathogenic SPTA mutations have been reported, this observation can be attributed to the effect of the cis inheritance of the Spa LEPRA allele either homozygous or heterozygous for this low expression polymorphism [25][26][27]. There is no definitive correlation between clinical phenotype and specific membrane proteins although a spectrin deficiency was found more frequently in children than in adults at presentation [83].…”

“…Finally, a spectrin alleles in patients with isolated spectrin deficiency and a co-inheritance of defective b spectrin gene have to be investigated at the molecular level to distinguish between a mutation or a polymorphic allele (e.g. spectrin a LEPRA ) responsible for the recessive pattern of inheritance [25,26,111]. SDS-PAGE can detect the typical hypoglycosylated CDAII band 3 (Figure 2a) if there is uncertainty between HS and CDAII for a patient.…”

Guidelines for the diagnosis and management of hereditary spherocytosis – 2011 update

“…Knowledge of the gene mutation does not influence the clinical management of the patient but analysis of the mutant protein gene in family studies can clarify one of the following conditions. The Spa LEPRA allele (LEPRA: Low Expression PRAgue) is prevalent among non-dominant HS (nd-HS) (Boivin et al, 1993;Dhermy et al, 2000;Wichterle et al, 1996). This allele remains silent when inherited by a normal individual.…”

Severe nondominant hereditary spherocytosis in an infant with coinheritance of three rare alpha‐spectrin gene defects

“…Thus, homozygosity for α LEPRA leads to marked deficiency of α‐spectrin in the affected child but normal spectrin content in heterozygous parents. Coinheritance of α LEPRA with another α‐spectrin frameshift or null mutation also leads to markedly decreased α‐spectrin and severe HS . Allele α LEPRA is associated in cis with a functionally neutral polymorphism, αBH (GCT > GAT codon 970), that is not responsible for HS but present in linkage disequilibrium with α LEPRA .…”