A Mutation in the E1α Subunit of Pyruvate Dehydrogenase Associated with Variable Expression of Pyruvate Dehydrogenase Complex Deficiency

Abstract

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...

Mutation analysis of the pyruvate dehydrogenase E1α gene in eight patients with a pyruvate dehydrogenase complex deficiency

“…Two of the eight mutations found in our patients (R263G and R302C) have already been described previously (Wexler et al, 1992;Chun et al, 1'993;Dahl et al, 1992b;De Meirleir et al, 1993). The clinical history of female patient 2 (R30;!C mutation) is very similar to already described patients carrying this mutation.…”

“…Cultured skin fibroblasts are most frequently used for diagnosis. As previously mentioned, most of the mutations in PDH complex deficiencies are found in the E l a m b u n i t of the complex; however, the expression of this gene at the mRNA level does not appear to be altered in most of the patients (Dahl et al, 1992a,b;Dahl and Brown, 1994;De Meirleir et al, 1992Chun et al, 1993;Wexler et al, 1992;Matthews et al, 1993;Hansen et al, 1993;Takakubo et al, 1993a,b;Endo et al, 1989Endo et al, , 1941. We describe the detection of mutations in the E,a gene of eight patients with a PDH complex deficiency.…”

Biochemical and genetic studies of four patients with pyruvate dehydrogenase E1α deficiency

“…Four mutations lie within this region in five unrelated patients. Indeed, the mutation R263G has been identified in five families, making it the most common PDH mutation to date (Chun et al 1993(Chun et al , 1995Wexler et al 1992;Lissens et al 1996; Table 2). The clinical histories of these patients are similar, except for our case 1 who died earlier than the other R263G cases.…”

“…The diagnosis of PDH deficiency depends on the measurement of residual enzyme activity in fresh lymphocytes, lymphoblastoid cell lines, cultured skin fibroblasts or muscle tissue. At least 70 patients with PDH deficiency have been reported so far and 52 different mutations in the coding region of the Ε1α subunit have been described (Kerr et al 1988Endo et al 1989Endo et al , 1991Dahl et al 1990Dahl et al , 1992Chun et al 1991Chun et al , 1993Chun et al , 1995Hansen et al 1991Hansen et al , 1993Hansen et al , 1994De Meirleir et al 1992Ito et al 1992Ito et al , 1995Wexler et al 1992Wexler et al , 1995Matthews et al 1993Matthews et al a, b, 1994Takakubo et al 1993Takakubo et al a, b, 1995Awata et al 1994;Dahl and Brown 1994;Fujii et al 1994;Naito et al 1994a, b;Hemalatha et al 1995;Lissens et al 1995Lissens et al , 1996Matsuda et al 1995;Tripatara et al 1996). Two mutations in E3 have also been identified (Liu et al 1993) but, so far, no molecular mutations have been reported that specifically affect the E1β subunit, E2, component X or PDH-phosphatase.…”

Pyruvate dehydrogenase deficiency: Molecular basis for intrafamilial heterogeneity

“…There are several reports of E l a deficiency associated with a decreased Elf3 immunoreactivity [5,12,24,[26][27][28]. These authors speculated that a mutation affecting the expression of one of the subunit proteins causes the remaining uncomplexed subunit to be unstable.…”