Rapid diagnosis of pyruvate and ketoglutarate dehydrogenase deficiencies in platelet-enriched preparations from blood

Abstract

Radiochemical methods are described in detail to measure the activities of the pyruvate dehydrogenase complex and of the ketoglutarate dehydrogenase complex in platelet-enriched fractions. Determinations can be completed in one day with as little as 5 ml of venous blood. Activities are proportional to the length of the incubation and the amount of tissue protein added, show appropriate dependence on added cofactors, are stable for up to 2 days at −20°C, and do not appear to be affected by diet. The pyruvate dehydrogenase complex appears to be fully activated (dephosphorylated) in these preparations. Activities were comparable in platelet-enriched fractions from 25 normal subjects and 25 patients with a variety of neurological and psychiatric diagnoses. Mean values (± S.E.M.) for these 50 individuals were 169 ± 9 pmol/min per mg protein for the pyruvate dehydrogenase complex and 535 ± 27 pmol/ min per mg protein for the ketoglutarate dehydrogenase complex. These values are comparable to those found in cultured skin fibroblasts with similar techniques. Deficient pyruvate dehydrogenase activity (19 ± 6 and 11 ± 4 pmol/min per mg protein) was demonstrated in platelet-enriched preparations from two brothers whose fibroblasts had previously been shown to be deficient in pyruvate dehydrogenase and who responded to a ketogenic diet. Experimental details critical to obtaining reproducible results with these methods are stressed (notably the crucial importance of maintaining the purity of the radioactive substrates). These techniques allow identification of patients with pyruvate dehydrogenase deficiencies within one day without requiring liver or muscle biopsy.