MUTATIONS IN PDX1, THE HUMAN LIPOYL-CONTAINING COMPONENT-X OF THE PYRUVATE-DEHYDROGENASE COMPLEX GENE ON CHROMOSOME 11P1, IN CONGENITAL LACTIC-ACIDOSIS

We have identified and sequenced a cDNA that encodes an apparent human orthologue of a yeast protein-X component (ScPDX1) of pyruvate dehydr ogenase multienzyme complexes. The new human cDNA that has been referr ed to as ''HsPDX1'' cDNA was cloned by use of the ''database cloning'' strategy and had a 1,506-bp open reading frame. The amino acid sequen ce of the protein encoded by the cDNA was 20% identical with that enco ded by the yeast PDX1 gene and 40% identical with that encoded by the lipoate acetyltransferase :component of the pyruvate dehydrogenase and included a lipoyl-bearing domain that is conserved in some dehydrogen ase enzyme complexes. Northern blot analysis demonstrated that the maj or HsPDX1 mRNA was 2.5 kb in length and was expressed mainly in human skeletal and cardiac muscles but was also present, at low levels, in o ther tissues. FISH analysis performed with a P1-derived artifical chro mosome (PAC)-containing HsPDX1 gene sublocalized the gene to 11p1.3. M olecular investigation of PDX1 deficiency in four patients with neonat al lactic acidemias revealed mutations 78del85 and 965del59 in a homoz ygous state, and one other patient had no PDX1 mRNA expression.