SPECTRIN α-CHAIN VARIANTS IN HEREDITARY ELLIPTOCYTOSIS / PYROPOIKILOCYTOSIS LACK SIMPLE CORRELATION BETWEEN MOLECULAR DEFECTS AND CLINICAL SEVERITY. 96

The clinical symptomatology differs widely among patients with hereditary elliptocytosis (HE): Silent HE, HE with mild hemolytic anemia, HE with infantile poikilocytosis and pyropoikilocytosis (HPP). Here we describe HE and HPP in 3 unrelated families.

Spectrin (Sp) was extracted from red cell membranes by low ionic strength. Tryptic digestion showed different variant Sp α proteins in the families(see table). Sp concentration measured by ELISA was in the normal range. DNA analysis (SSCP, DNA sequencing) showed different point mutations in exon 2 and 6 of α-spectrin. In family 1 the defect has been previously described as Sp α-Lyon by MorlΘ et al. [J Clin Invest(1990) 86: 548-554]. Sp dimer was increased to 50% in two severely affected and in one asymptomatic carrier of the Sp α-defect. Sp dimer was also distinctly increased to 34% in one asymptomatic baby described by MorlΘ et al. and thus Sp dimer content does not correlate to the clinical severity. The mutation in family 2 (two Black Americans) is frequently found in Blacks. Heterozygous carriers of this defect have mild HE or are asymptomatic carriers of HPP. One of our patient had a distinct hemolysis during neonatal period which slowly improved in the second half of the first year. In family 3, the son is heterozygous for the defect in exon 2 and has HPP. Until now, HPP was described only in homozygous or double heterozygous patients. Thus, our patient has probably a second yet undetected mutation. As neither of his parents is affected, the identified Sp α-defect must have arisen de novo. The Arg28 is replaced by several other amino acids in patients with HE and HPP, indicating that codon 28 might be a hot spot of mutation. The results confirm the high frequency of N-terminal α-spectrin defects in HE and HPP with increased spectrin dimer content. However, there is only a poor relation between the primary defect and clinical severity, pointing to additional factors that modify the clinical expression. Sp α^LELY, a low expression allele associated with mutations in exon 40, intron 45 and partial skipping of exon 46, has been described as a modifier of clinical severity in HE. Up to now we did not find a relation between the occurence of Sp α^LELY mutations and disease severity.

Table 1