A novel syndrome affecting multiple mitochondrial functions, located by microcell-mediated transfer to chromosome 2p14-2p13.
We have studied cultured skin fibroblasts from three siblings and one unrelated individual, all of whom had fatal mitochondrial disease manifesting soon after birth. After incubation with 1 mM glucose, these four cell strains exhibited lactate/pyruvate ratios that were six times greater than those of controls. On further analysis, enzymatic activities of the pyruvate dehydrogenase complex, the 2-oxoglutarate dehydrogenase complex, NADH cytochrome c reductase, succinate dehydrogenase, and succinate cytochrome c reductase were severely deficient. In two of the siblings the enzymatic activity of cytochrome oxidase was mildly decreased (by approximately 50%). Metabolite analysis performed on urine samples taken from these patients revealed high levels of glycine, leucine, valine, and isoleucine, indicating abnormalities of both the glycine-cleavage system and branched-chain alpha-ketoacid dehydrogenase. In contrast, the activities of fibroblast pyruvate carboxylase, mitochondrial aconitase, and citrate synthase were normal. Immunoblot analysis of selected complex III subunits (core 1, cyt c(1), and iron-sulfur protein) and of the pyruvate dehydrogenase complex subunits revealed no visible changes in the levels of all examined proteins, decreasing the possibility that an import and/or assembly factor is involved. To elucidate the underlying molecular defect, analysis of microcell-mediated chromosome-fusion was performed between the present study's fibroblasts (recipients) and a panel of A9 mouse:human hybrids (donors) developed by Cuthbert et al. (1995). Complementation was observed between the recipient cells from both families and the mouse:human hybrid clone carrying human chromosome 2. These results indicate that the underlying defect in our patients is under the control of a nuclear gene, the locus of which is on chromosome 2. A 5-cM interval has been identified as potentially containing the critical region for the unknown gene. This interval maps to region 2p14-2p13.
Seyda
A
A
Metabolism Research Programme, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
Newbold
R F
RF
Hudson
T J
TJ
Verner
A
A
MacKay
N
N
Winter
S
S
Feigenbaum
A
A
Malaney
S
S
Gonzalez-Halphen
D
D
Cuthbert
A P
AP
Robinson
B H
BH
D000596:Amino Acids / Q000097:blood; D000818:Animals; D002478:Cells, Cultured; D002872:Chromosome Deletion; D002889:Chromosomes, Human, Pair 2 / Q000235:genetics*; D017809:Fatal Outcome; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D005816:Genetic Complementation Test; D006801:Humans; D007223:Infant; D008297:Male; D008928:Mitochondria / Q000201:enzymology / Q000473:pathology*; D009154:Mutation; D010641:Phenotype; D021101:Radiation Hybrid Mapping; D013577:Syndrome
D000596:Amino Acids