Ruth M. Brown

X-Chromosome localization of the functional gene for the E1α subunit of the human pyruvate dehydrogenase complex

The functional gene locus for the E1 alpha subunit of the human pyruvate dehydrogenase complex has been localized to the p22.1-22.2 region of the X chromosome by in situ hybridization and analysis of somatic cell hybrids with various human X-chromosome rearrangements. Another locus showing significant cross-hybridization with an E1 alpha cDNA probe was detected on chromosome 4, in the region q22. The X-chromosome localization of the pyruvate dehydrogenase E1 alpha subunit gene provides a number of possible explanations for the clinical and biochemical variability which is a major feature of human pyruvate dehydrogenase deficiency.

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.

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.

Localization of the human dihydropteridine reductase gene to band p15.3 of chromosome 4 byin situ hybridization

We report the localization of the gene for dihydropteridine reductase (DHPR) to the human chromosome region 4p15.3 by in situ hybridization using a cDNA probe to the enzyme. The distal end of the short arm of chromosome 4 is of considerable interest because the gene responsible for Huntingtons disease is located in this region. Although this part of the chromosome is being extensively studied, DHPR is the first well-characterised gene to be assigned to the region. Restriction enzyme fragment length polymorphisms have been detected with a number of restriction endonucleases, including AvaII and MspI. These features may make the DHPR cDNA clone a useful probe not only for prenatal diagnosis of DHPR deficiency but also for linkage studies of Huntingtons disease.

Carcinoembryonic antigen (CEA) expression in somatic cell hybrids.

Five hybrids (LSB) were formed between LS174T, a human CEA-producing colonic tumor cell line, and BU25.CAPR, a HeLa derivative which does not produce CEA. All five hybrids produce CEA, but less per cell than LS174T. Approximately 10 % of the chromosomes have been lost from these hybrids. In an attempt to map the gene(s) coding for the protein moiety of CEA, 7 LSPG and 28 LSR hybrids were formed between LS174T and PG19, a mouse melanoma cell line, and LS174T and RAG, a mouse kidney adenocarcinoma cell line, respectively. These hybrids retain between 4 and 21 human chromosomes, and each human chromosome is represented in at least seven hybrids. Two hybrids appeared to produce trace amounts of CEA. These results might represent repression by the mouse genome of CEA production or the production of a structurally abnormal CEA molecule.

Isolation of human chromosome 21 sequences and their application to in situ hybridization

SummaryWe report the isolation of 50 independent unique sequences from a human chromosome 21 library (identification code LA21 NSO1). These sequences were individually assigned to chromosome 21 using a mouse-human somatic hybrid cell line, WAVR 4d-F94a. Use of these unique clones as a mixture of probes for in situ hybridization of human metaphase chromosomes demonstrated strong signals on chromosome 21. These unique DNA sequences should provide useful tools for structural and functional analysis of human chromosome 21. The use of these sequences for the detection of Down syndrome is discussed.