Spectrin Tunis (alpha I/78): a new alpha I variant that causes asymptomatic hereditary elliptocytosis in the heterozygous state.

Spectrin Tunis (alpha 1/78) was found in the heterozygous state in a young white North-African man and his mother. Both of them presented with mild elliptocytosis. Using one-dimensional electrophoresis, a sharp 78 kd fragment was present with a reciprocal decrease of the alpha I 80 kd domain. Kinetic analysis unambiguously confirmed that the 78 kd fragment developed at the expense of the alpha I 80 domain. The alpha I 74 kd peptide was not flanked with a peptide lacking a 2 kd fragment. From this fact, it could be inferred that the site for additional proteolysis is located upstream from arginyl residue 39 and, more precisely, should lie 10 to 20 amino-acid residues (-2 kd) from the alpha-chain N-terminus. The percentage of spectrin dimers in 4 degrees C extracts was high (over 40%), contrasting with the absence of clinical symptoms related to elliptocytosis. This is the first mutation responsible for elliptocytosis found in Tunisia.