Inborn errors of the pyruvate dehydrogenase complex (PDC) are associated with lactic acidosis, neuroanatomic defects, developmental delay, and early death. PDC deficiency is a clinically heterogeneous disorder, with most mutations located in the coding region of the X-linked alpha subunit of the first catalytic component, pyruvate dehydrogenase (E1). Treatment of E1 deficiency hs included cofactor replacement, activation of PDC with dichloroacetate, and ketogenic diets. In this report, we describe the outcome of ketogenic diet treatment in seven boys with E1 deficiency. These patients were divided into two groups based on their mutations (R349H, three patients; and R234G, four patients, two sibling pairs). All seven patients received ketogenic diets with varying degrees of carbohydrate restriction. Clinical outcome was compared within each group and between siblings as related to the intensity and duration of dietary intervention. Subjects who either had the diet initiated earlier in life or who were placed on greater carbohydrate restriction had increased longevity and improved mental development. Based on the improved outcomes of patients with identical mutations, it appears that a nearly carbohydrate-free diet initiated shortly after birth may be useful in the treatment of E1 deficiency.

Amintr acid sequence ecmp~risan of'8 tl nnd 6 JsubunEta of the a-kcta aeici dchydrngenanc (E,] component af thr pyruvutc dehydruacnuac complcr and brenehcd-ehrrin wkc~n ticid dckydroganurc enmglox from multiple xpcies was performed by cemputcr analysis. In addition to 2 prcviaullly reeegnircd rcpianr ot'hamaisgy in the 01 subunit, a 3rd rct$an oP cxtcnrlvc homolapy was identified in E,a, and miry bc one of tht? riru invDlvcd in subunit interaction. S,fl containr 4 rcyionr of extensive homology. Region I contains IO amino nridr that WC Ramolo#juur; ta a I&amino acid stretch in Ekh~rieiritr rdi/i E,. Regianr 1 and 3 hrvc scquencc homoiagicn with ether dehydregcnam~ sugyrrting that rhcro fcgionr may be involved in eatnlywix.Byruvntc dchydrogcnaxc: Pyruvntc dchydrelgenttbc complex: Urrnehcd-chain a&eta acid dchydrogcnusc complex: cl-Keto acid dchydregcnrsc corns plcx; Amino acid sequcncccomparioen INTRODUCTIONThe mammalian pyruvate dehydrogcnase complex (PDC) is a mitochondrial multienzyme complex that ' catalyzes the conversion of pyruvate to acetyl-CoA [1,2]. The complex consists of 3 catalytic and 2 regulatory components, and a protein X component. In plant {3], eukaryotic, and some prokaryotic species [4], the first catalytic component, pyruvate dehydrogcnase, (El) (py, uvate: lipoamide 2.oxidoreductase, EC 1.2.4.1), is composed of 2 non-identical 01 and P subunits which form a heterotetramer. El, which requires thiamin pyrophosphate as a cofactor, catalyzes the oxidative decarboxylation of pyruvate according to the following 2 partial reactions.amino acid residues Elas identified critical amino acids in the El heterotetramer that are critical For enzyme function [7]. Recent studies have shown that El& but not ElcrI is protected from trypsin digestion when bound to dihydrolipoyl acetyltransferase (I%), the 2nd catalytic component of PDC, suggesting that EIP binds to EZ [8]. Structure-function analysis has been facilitated by the cloning of both the (Y [4,9-111 and I3 [4,12,13] subunits of PDC from multiple species. However, the critical amino acid residues in the functional domains of E,DL and I&P remain unidentified. In the present study, we have used computer analysis to identify several regions of the (Y and /3 subunits that are highly conserved not only in all the known sequences of the 2 subunits of PDC from various species, but also in those of the branched-chain ol-keto acid dlhydrogenase complexes (BCKDC) in both prokaryotic and eukaryotic species. Similarities with other proteins suggest that one of the conserved domains may play a critical role in the oxidative decarboxylation of the 01-keto acids. Based on limited data, it has been postulated that reaction (I) is carried out by the (v subunit, and reaction (ii) by the P subunit [5]. Etu! activity is regulated by phosphorylation-dephosphorylation by a specific El kinase and phosphatase [l]. Sequence comparison of multiple thiamine-dependent enzymes has allowed for the identification of a putative thiamin gyrophosphate binding motif in Ela, [6]. Chemica...

ABSTRACT. Defects in pyruvate dehydrogenase, the first catalytic component of the pyruvate dehydrogenase complex, are the most common cause of pyruvate dehydrogenase complex deficiency. A family with variable pyruvate dehydrogenase complex deficiency had been described in which cultured skin fibroblast s of affected family members had normal pyruvate dehydrogenase complex activity, but different tissues and blood lymphocytes had significantly diminished activities. Enzymatic activity and immunoblot studies indicated that pyruvate dehydrogenase was affected. Further evidence is presented here showing that the defect affecting pyruvate dehydrogenase complex activity is posttranscriptional. Sequencing of the coding region of the a -subunit of pyruvate dehydrogenase revealed a point mutation in the codon for amino acid 234 resulting in a substitution of glycine for arginine. Stud y of other members of the family suggested that this mutation is inherited in a sex-linked mode. The point mutation is located in a highly conserved region of the pyruvate dehydrogenase a-subunit gene that contains both hydrophobic and positively charged amino acid residues. Variable expression of pyruvate dehydrogenase complex deficiency in this case may be due to instability of the pyruvate dehydrogenase heterotetramer in specific tissues because of a disruption in subunit-subunit interaction. (Pediatr Res 32: 169-174,1992) Abbreviations Ell pyruvate dehydrogenase E1a , a -subunit of E. E 1,8 , ,8-subunit of E 1 E3, dihydrolipoamide dehydrogenase PDC, pyruvate dehydrogenase complex PCR, polymerase chain reaction Th e PDC is a nuclear-encoded mitochondrial enzyme complex t hat catalyzes the conversion of pyruvate to acetyl-CoA. PDC consists of thre e catalytic components: E 1 (pyruvate:lipoam ide 2-oxidoreductase, EC 1.2.4.1.), dihydrolipoamide acetyltransferase, and E 3 as well as a prot ein X that forms part of the comp lex. The E 1 com ponent consists of two subunits encoded by different genes, a and (3, which com bine as a heterotetramer. Regulation of the complex is via phosphorylation by Ei-kinase and dephosphorylation by phospho E j-phosphatase of th ree specific serine residues on Ela (1,2).PDC deficiency, an inborn error of pyruvate metabolism, is manifested by elevated serum pyruvat e and lactate. Individuals with PDC deficiency have varying levels of neur ologic dysfunction ranging from mild ataxia to neuroanatom icallesions incompatible with life (3, 4). Most PDC mutations affect the E1 component of PDC (5, 6). Recently, identification of mut ations affecting Ela has been facilitated by the cloning and charac terization of cDNA (7-10) and genomic DNA for Eta (1 1, 12). By in situ hybridization, the Ela gene has been localized to the X chromosome (13). Mutations involving deletions or single base changes have been found on the a -subunit (14-17).Previously, we described a family with PDC deficiency in which variable PDC enzymatic activity was observed in different tissues (18). The proband was found to have minimal PDC activi...

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