[Molecular basis and pathophysiology of red cell enzymopathies]

Recent progress in the molecular analysis of red cell enzymopathies showed over 160 mutations in the 10 distinct genes which were essential in red cell metabolisms. In addition, since three-dimensional structure of several enzymes including pyruvate kinase (PK) and glucose-6-phosphate dehydrogenase (G6PD) have been elucidated from X-ray crystallographic studies, the effect of amino acid substitutions on enzyme activity became predictable in some extent. On the contrary, the mechanism of hemolysis remains still unclear. To clarify the pathophysiology of red cell enzymopathies, establishment of an animal model have been long awaited. Recently we discovered the novel mice model of PK deficiency. The mutant mice with splenomegaly and nonspherocytic hemolytic anemia in an inbred colony of the CBA strain were enzymatically diagnosed as PK deficiency. A homozygous missense mutation was identified in the red cell (R)-type PKcDNA sequence of the mutant, and it caused a single amino acid substitution near the substrate binding site of PK. The erythroid-progenitor cell number increased in spleen of the mutant mice to a level approximately 66 times higher than in normal CBA mice, suggesting that compensatory extramedullary erythropoiesis in the spleen of the mutant mice might partly compensate the anemia. The mutant mice will be useful as an experimental model for understanding the pathophysiology of this disorder.