H.-H. M. Dahl

X-linked pyruvate dehydrogenase E1α subunit deficiency in heterozygous females : variable manifestation of the same mutation

SummaryThree female patients are described with pyruvate dehydrogenase (PDH) deficiency as a result of mutation in the X-linked gene for the E1α subunit of the complex. Two of these patients illustrate typical presentations of PDH E1α deficiency, with severe neurological dysfunction, degenerative changes and developmental anomalies in the brain, together with variable lactic acidosis. The third patient extends the known spectrum of the condition to include mild to moderate mental retardation and seizures in an adult. All three patients have the same mutation in the PDH E1α gene. This mutation, a C-to-T substitution in a CpG dinucleotide in amino acid codon 302 (designated R302C), results in the replacement of arginine by cysteine at this position. The mildly affected adult was the mother of one of the other patients, making this the first described instance of mother-to-daughter transmission of a mutation causing PDH E1α deficiency. The genetic basis of the variable expression of X-linked PDH E1α deficiency in heterozygous females is discussed.

Characterization of the mutations in three patients with pyruvate dehydrogenase E1α deficiency

SummaryThe human pyruvate dehydrogenase complex catalyses the oxidative decarboxylation of pyruvate to acetyl-CoA. Defects in several of the seven subunits have been reported, but the majority of mutations affect the E1 component and especially the E1α subunit. However, the clinical presentation of patients with pyruvate dehydrogenase E1α deficiency is extremely variable. Dependency of the brain on pyruvate dehydrogenase activity and localization of the gene for the somatic form of the pyruvate dehydrogenase E1α subunit to the X chromosome provide the basis for a better understanding of the variation in the clinical manifestations. Further understanding of the function and interaction of subunits and the pathophysiology of pyruvate dehydrogenase deficiency necessitates the characterization of mutations in the pyruvate dehydrogenase complex. We report the analysis of three patients with pyruvate dehydrogenase E1α deficiency. One female has a three base pair deletion which affects dephosphorylation of the subunit. Of two males analysed, one has a two base pair deletion causing a shift in the reading frame. The other has a base change, resulting in an Arg to His substitution. All three mutations are located near the carboxyl terminus of the subunit.

Pyruvate dehydrogenase E1α subunit genes in the mouse: Mapping and comparison with human homologs

Two gene loci for the E1α subunit of the pyruvate dehydrogenase (PDH) complex have been mapped in the mouse by in situ hybridization. One locus maps to the X chromosome in the region F3–F4, the other to chromosome 19, in band B close to the centromere. This arrangement is exactly comparable to the situation in man where there is an X-linked PDH E1α locus and an autosomal locus on chromosome 4. Comparison of the regional localization of the human and mouse X-linked PDH E1α genes provides further information concerning sites of rearrangement of segments of the X chromosome during mammalian evolution. The human autosomal PDH E1α gene is a “processed” gene, which lacks the introns that are present in the X-linked gene. It codes for a testis-specific E1α subunit that is only expressed after the onset of spermatogenesis. The comparative mapping results in the mouse suggest that the genetic organization and pattern of expression of the two PDH E1α genes is the same in the two species.

Detection and localization of base changes in RNA using a chemical cleavage method.

The detection of base changes in DNA and RNA is of central importance in genetic research. Mismatched cytosines and thymines in heteroduplex DNA molecules show increased chemical reactivity with hydroxylamine and osmium tetroxide, respectively, and the DNA can then be specifically cleaved at the modified nucleotides. We show here that mismatched cytosines and thymines can be detected and located directly in RNA: DNA heteroduplex molecules. In order to detect guanosine and adenosine base changes the complementary cDNA strand must be analyzed. In addition, the sensitivity of the technique can be increased by employing the polymerase chain reaction. To test the fidelity of this method a number of known or predicted mutations were analyzed. These include single point mutations in the human collagen alpha 1(I) and rat phenylalanine hydroxylase mRNA, two engineered point mutations in a mouse collagen alpha 1(I) mRNA, and a deletion in a human collagen alpha 2(I) mRNA. All known base changes were detected and correctly localized. In addition, the predicted base changes were confirmed.