HEREDITARY HEMOLYTIC-ANEMIA CAUSED BY DIVERSE POINT MUTATIONS OF PYRUVATE-KINASE GENE FOUND IN JAPAN AND HONG-KONG

We identified four distinct point mutations in homozygous pyruvate kin ase (PK) variants in Japanese and Chinese patients with chronic nonsph erocytic hemolytic anemia. All gene abnormalities were missense mutati ons that caused single amino acid substitutions. 1261A (Q421K) and 143 6A (R436H), which were identified in PK Sendai and PK Shinshu, had bee n found in unrelated Japanese and Amish PK variants, respectively. The clinical severity and extremely low residual erythrocyte PK activity of PK Shinshu as well as of the Amish PK might be caused partly by abe rrant splicing, because the 1436A mutation changes a nucleotide at the last nucleotide in the exon 10. Recently, we diagnosed a 42-year-old Japanese woman with chronic nonspherocytic hemolytic anemia as having a homozygous PK deficiency. DNA sequencing of the variant PK gene show ed a homozygous missense mutation at 1403GCT --> GTT, resulting in a s ingle amino acid substitution from 468Ala --> Val. The gene mutation i s likely to impair the allostericity of this enzyme, speculated from t he tertiary structure. A homozygous missense mutation in PK Hong Kong, a boy of a non-Han southern Chinese minority group, was identified in exon 7 of the human L-PK gene, 941AtT --> ACT, resulting in a single amino acid substitution from 314Ile --> Thr. The R-PK activity is expe cted to be severely affected, because the mutated amino acid residue i s located between the 313 Lys and the 315 Glu, which are very importan t for acid-base catalysis and magnesium binding, respectively. Both th e R- and M2-type PK were shown by polyacrylamide gel electrophoresis o f the PK Hong Kong erythrocyte lysate, and this is the first report of a homozygous individual whose erythrocytes contain the immature (M2)- type isozyme. (C) 1994 by The American Society of Hematology.