PYRUVATE-DEHYDROGENASE COMPLEX DEFICIENCY AND ABSENCE OF SUBUNIT-X

The pyruvate dehydrogenase complex (PDHc) is a multienzyme complex con sisting of three catalytic and two regulatory enzymes, as well as a le ss well defined subunit called protein X. PDHc deficiency is a common cause of congenital lactic acidosis. Most patients with PDH deficiency have a mutation in the alpha chain of the PDH E1 enzyme. Very few pat ients have been described in whom the basic defect of a PDH deficiency is situated in the X protein. We studied a boy with severe lactic aci dosis and developmental delay in whom a deficiency of PDH activity led to further investigations. Immunochemical analysis with anti-PDHc ant ibodies demonstrated an absence of the X component. This report is the fourth family in which an abnormal protein X has been found. In cases with PDH deficiency where no mutation of the PDHE1 alpha gene is foun d, further investigations by means of immunoblotting with specific ant ibodies against the different subunits should be performed.