Carrier detection in X-linked recessive (Duchenne) muscular dystrophy: pyruvate kinase isoenzymes and creatine phosphokinase in serum and blood cells.

Allosterism allows individual assay of both isoenzymes, one abundant in muscle, of pyruvate kinase (PK), recently reported superior to serum creatine phosphokinase (CPK) in detecting patients with and female carriers of X-linked recessive (Duchenne) muscular dystrophy (DMD). Extensive comparative studies did not support these findings and confirmed the marked superiority of CPK over rariants of PK or other enzymes in sensitivity, stability and convenience. Deducting the adenylate kinase increment (AKI) further refined the CPK assay, eliminating the effect of haemolysis in diagnosis and enabling studies of blood cell content. Both leucocytes and erythrocytes liberated PK and lactate dehydrogenase (LDH) after brief chilling or disruption. Only erythrocytes showed a CPK content, however, constantly adjusted to match that of serum as if by free cell membrane passage, but less accomodating to a sudden large influx of CPK than of LDH, where an apparent buffering effect could account for differences in clinical response.