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Biomedical subjects

D C Wallace

Publications and source records attributed to D C Wallace.

At least 109 records · Page 6Linked to original sources
PubMed1995

Dilated cardiomyopathy and neonatal lethality in mutant mice lacking manganese superoxide dismutase.

The Sod2 gene for Mn-superoxide dismutase (MnSOD), an intramitochondrial free radical scavenging enzyme that is the first line of defense against superoxide produced as a byproduct of oxidative phosphorylation, was inactivated by homologous recombination. Homozygous mutant mice die within the first 10 days of life with a dilated cardiomyopathy, accumulation of lipid in liver and skeletal muscle, and metabolic acidosis. Cytochemical analysis revealed a severe reduction in succinate dehydrogenase (complex II) and aconitase (a TCA cycle enzyme) activities in the heart and, to a lesser extent, in other organs. These findings indicate that MnSOD is required for normal biological function of tissues by maintaining the integrity of mitochondrial enzymes susceptible to direct inactivation by superoxide.

Acidosis↗
PubMed1995

Marked increase in mitochondrial DNA deletion levels in the cerebral cortex of Huntington's disease patients.

To determine if somatic mtDNA mutations might contribute to the neurodegeneration observed in Huntington's disease (HD), we quantitated the amount of the common mitochondrial 4977 nucleotide pair deletion (mtDNA4977) in cortex and putamen of HD patients and age-matched controls by the serial dilution-polymerase chain reaction method. Cortical deletion levels were analyzed in the temporal, frontal, and occipital lobes. HD temporal lobes had an 11-fold greater mean mtDNA4977 deletion level than age-matched controls, and HD frontal lobes had fivefold greater levels. HD occipital lobe and putamen deletion levels were comparable with control levels. These results support the hypothesis that HD is associated with elevated cortical mtDNA damage.

Adult↗
PubMed1995

Mitochondrial encephalomyopathy associated with a single nucleotide pair deletion in the mitochondrial tRNALeu(UUR) gene.

The investigation of pathogenic mitochondrial DNA (mtDNA) mutations has revealed a complex relation between patient genotype and phenotype. For unknown reasons, some mtDNA mutations produce specific clinical manifestations such as chronic progressive external ophthalmoplegia; myoclonic epilepsy and ragged-red fiber disease (MERRF); and mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). To enhance our understanding of the association between genotype and phenotype, we investigated a patient with mitochondrial encephalomyopathy and severe cerebral calcifications for a mtDNA mutation. There was a deletion of one of three T:A nucleotide pairs in the tRNALeu(UUR) gene of the mtDNA involving positions 3271 to 3273. Pedigree analysis suggested that this mutation may have occurred spontaneously in the proband. This analysis represents the smallest mtDNA deletion observed to date and is the first deletion identified within a mitochondrial tRNA. This observation emphasizes the importance of delineating the precise mutation responsible for an oxidative phosphorylation disease for patient diagnosis as well as for genetic counseling of maternal lineage relatives.

Adult↗
PubMed1995

Analysis of mtDNA variation in African populations reveals the most ancient of all human continent-specific haplogroups.

mtDNA sequence variation was examined in 140 Africans, including Pygmies from Zaire and Central African Republic (C.A.R.) and Mandenkalu, Wolof, and Pular from Senegal. More than 76% of the African mtDNAs (100% of the Pygmies and 67.3% of the Senegalese) formed one major mtDNA cluster (haplogroup L) defined by an African-specific HpaI site gain at nucleotide pair (np) 3592. Additional mutations subdivided haplogroup L into two subhaplogroups, each encompassing both Pygmy and Senegalese mtDNAs. A novel 12-bp homoplasmic insertion in the intergenic region between tRNA(Tyr) and cytochrome oxidase I (COI) genes was also observed in 17.6% of the Pygmies from C.A.R. This insertion is one of the largest observed in human mtDNAs. Another 25% of the Pygmy mtDNAs harbored a 9-bp deletion between the cytochrome oxidase II (COII) and tRNA(Lys) genes, a length polymorphism previously reported in non-African populations. In addition to haplogroup L, other haplogroups were observed in the Senegalese. These haplogroups were more similar to those observed in Europeans and Asians than to haplogroup L mtDNAs, suggesting that the African mtDNAs without the HpaI np 3592 site could be the ancestral types from which European and Asian mtDNAs were derived. Comparison of the intrapopulation sequence divergence in African and non-African populations confirms that African populations exhibit the largest extent of mtDNA variation, a result that further supports the hypothesis that Africans represent the most ancient human group and that all modern humans have a common and recent African origin. The age of the total African variation was estimated to be 101,000-133,000 years before present (YBP), while the age of haplogroup L was estimated at 98,000-130,000 YBP. These values substantially exceed the ages of all Asian- and European-specific mtDNA haplogroups.

Africa↗
PubMed1995

Oxidative phosphorylation diseases and cerebellar ataxia.

Oxidative phosphorylation (OXPHOS) diseases can be caused by mutations in nuclear genes or mitochondrial DNA (mtDNA) genes. mtDNA mutations include complex mtDNA rearrangements in which large segments of mtDNA are duplicated or deleted and point mutations in which single nucleotide substitutions occur within transfer RNA (tRNA) genes, ribosomal RNA (rRNA) genes, or mitochondrial genes encoding OXPHOS polypeptides. Although over 30 pathogenic mtDNA point mutations and over 60 different types of mtDNA deletions are known (Shoffner and Wallace, 1995; Wallace et al., 1994), only a subset of these mutations are associated with cerebellar ataxia. This review focuses on the clinical, biochemical, and genetic features of OXPHOS diseases caused by mtDNA mutations in which ataxia is a common manifestation.

Adult↗
PubMed1994

Marked changes in mitochondrial DNA deletion levels in Alzheimer brains.

Levels of the common 4977 nucleotide pair (np) mitochondrial DNA (mtDNA) deletion (mtDNA4977) were quantitated in the cortex, putamen, and cerebellum of patients with Alzheimer disease (AD) and compared to age-matched controls. Although cerebellum deletion levels were comparably low in AD patients and controls of all ages, cortical deletion levels were clearly different. The levels of mtDNA deletions in control brains started low, but rose markedly after age 75, while those of AD patients started high and declined to low levels by age 80. Choosing age 75 to arbitrarily delineate between younger and older subjects, younger patients had 15 times more mtDNA deletions than younger controls, while older patients had one-fifth the deletion level of older controls. Younger AD patients also had fourfold more deletions than older AD patients. These results support the hypothesis that OXPHOS defects resulting from somatic mtDNA mutations may play a role in AD pathophysiology.

Age Factors↗
PubMed1994

Mitochondrial DNA sequence variation in human evolution and disease.

Germ-line and somatic mtDNA mutations are hypothesized to act together to shape our history and our health. Germ-line mtDNA mutations, both ancient and recent, have been associated with a variety of degenerative diseases. Mildly to moderately deleterious germ-line mutations, like neutral polymorphisms, have become established in the distant past through genetic drift but now may predispose certain individuals to late-onset degenerative diseases. As an example, a homoplasmic, Caucasian, tRNA(Gln) mutation at nucleotide pair (np) 4336 has been observed in 5% of Alzheimer disease and Parkinson disease patients and may contribute to the multifactorial etiology of these diseases. Moderately to severely deleterious germ-line mutations, on the other hand, appear repeatedly but are eliminated by selection. Hence, all extant mutations of this class are recent and associated with more devastating diseases of young adults and children. Representative of these mutations is a heteroplasmic mutation in MTND6 at np 14459 whose clinical presentations range from adult-onset blindness to pediatric dystonia and basal ganglial degeneration. To the inherited mutations are added somatic mtDNA mutations which accumulate in random arrays within stable tissues. These mutations provide a molecular clock that measures our age and may cause a progressive decline in tissue energy output that could precipitate the onset of degenerative diseases in individuals harboring inherited deleterious mutations.

Amino Acid Sequence↗
PubMed1994

Cytoplasmic transfer of the mtDNA nt 8993 T-->G (ATP6) point mutation associated with Leigh syndrome into mtDNA-less cells demonstrates cosegregation with a decrease in state III respiration and ADP/O ratio.

A point mutation in the mtDNA-encoded ATP6 gene (T-->G at nt 8993) associated with Leigh syndrome in two pedigrees was found to decrease ADP-stimulated (state III) respiration and the ratio of ADP molecules phosphorylated to oxygen atoms reduced (ADP/O ratio) but did not affect 2,4-dinitrophenol (DNP)-uncoupled respiration, suggesting a defective mitochondrial H(+)-translocating ATP synthase. Intact mitochondria isolated from patient and control lymphoblastoid cell lines were tested for state III, ADP-limited (state IV), and DNP-uncoupled respiration with various substrates. Mitochondria isolated from patient lymphoblasts harboring 95-100% of mtDNAs carrying the nt 8993 T-->G mutation showed state III respiration rates 26-50% lower than controls while having normal DNP-uncoupled rates. This resulted in state III/DNP ratios of 0.52-0.70 in patient mitochondria versus 0.88-0.97 in controls. The ADP/O ratio was also decreased 30-40% in patient mitochondria. Patient lymphoblasts heteroplasmic for the nt 8993 mutation were enucleated by using Percoll gradients and the cytoplasts were fused to mtDNA-deficient (rho 0) cells by electric shock. Cybrid clones homoplasmic for the wild-type nucleotide (T) at nt 8993 gave state III/DNP and ADP/O ratios similar to those of control cybrids, whereas cybrid clones homoplasmic for the mutant nucleotide (G) showed a 24-53% reduction in state III respiration, a state III/DNP ratio of 0.53-0.64, and a 30% decrease in the ADP/O ratio. Thus, the reduced state III respiration rates and ADP/O ratios are linked to the T-->G mutation at nt 8993.

DNA, Mitochondrial↗
PubMed1994

Epidemic neuropathy in Cuba not associated with mitochondrial DNA mutations found in Leber's hereditary optic neuropathy patients. Cuba Neuropathy Field Investigation Team.

An epidemic neuropathy in Cuba has caused bilateral optic neuropathies in more than 26,000 people during the past three years. Various pathogenetic factors have been proposed, including toxins, nutritional deficiencies, and an underlying genetic predisposition involving mitochondrial DNA. As part of a case-control collaborative investigation, 135 Cuban blood samples were analyzed for the most common mitochondrial DNA mutations associated with Leber's hereditary optic neuropathy. None of the participants tested were found to have the mitochondrial DNA mutations at nucleotide positions 11778, 3460, 14484, 7444, or 9804. Of 57 definite case subjects and 69 normal control subjects, three case and three control subjects had the mutation at nucleotide position 9438, three different case and three different control subjects had the mutation at position 13708, and one case and one control subject had the mutation at position 15257 in association with the mutation at position 13708. The most common mitochondrial DNA mutations associated with Leber's hereditary optic neuropathy do not appear to be contributing factors in the epidemic neuropathy in Cuba. We also identified a large Cuban family with maternally related members who experienced visual loss consistent with the diagnosis of Leber's hereditary optic neuropathy. Maternal family members harbored the highly pathogenetic mutation at nucleotide position 11778.

Adolescent↗
PubMed1994

A mitochondrial DNA mutation at nucleotide pair 14459 of the NADH dehydrogenase subunit 6 gene associated with maternally inherited Leber hereditary optic neuropathy and dystonia.

A five-generation Hispanic family expressing maternally transmitted Leber hereditary optic neuropathy and/or early-onset dystonia associated with bilateral basal ganglia lesions was studied. Buffy coat mitochondrial DNA (mtDNA) from a severely affected child was amplified by the polymerase chain reaction and greater than 90% sequenced. The mtDNA proved to be a Native American haplogroup D genotype and differed from the standard "Cambridge" sequence at 40 nucleotide positions. One of these variants, a G-to-A transition at nucleotide pair (np) 14459, changed a moderately conserved alanine to a valine at NADH dehydrogenase subunit 6 (ND6) residue 72. The np 14459 variant was not found in any of 38 Native American haplogroup D mtDNAs, nor was it detected in 108 Asian, 103 Caucasian, or 99 African mtDNAs. Six maternal relatives in three generations were tested and were found to harbor the mutation, with one female affected with Leber hereditary optic neuropathy being heteroplasmic. Thus, the np 14459 G-to-A missense mutation is specific to this family, alters a moderately conserved amino acid in a complex I gene, is a unique mtDNA variant in Native American haplogroup D, and is heteroplasmic, suggesting that it is the disease-causing mutation.

Adenine↗
PubMed1994

Mitochondrial myopathy with anemia, cardiomyopathy, and lactic acidosis: a distinct late onset mitochondrial disorder.

A 40-year-old woman presented with profound muscle weakness resulting in failure to wean from a ventilator and persistent lactic acidosis after having recovered from a pneumonia complicated by adult respiratory distress syndrome, myocardial infarction, renal failure and shock. She had a 28 year history of chronic anemia and exercise intolerance. Anemia and thrombocytopenia persisted after admission. Nonobstructive hypertrophic cardiomyopathy was present. A stroke-like episode occurred. A mitochondrial myopathy with deficiencies in complexes IV and II was demonstrated, but no DNA defect has yet been found. This patient represents a distinct clinical presentation of a mitochondrial disorder characterized by late onset mitochondrial myopathy, chronic anemia, cardiomyopathy, and lactic acidosis.

Acidosis, Lactic↗
PubMed1994

Steady state levels of mitochondrial and nuclear oxidative phosphorylation transcripts in Kearns-Sayre syndrome.

The steady state levels of both mitochondrial and nuclear transcripts were examined in a Kearns-Sayre syndrome patient harboring a heteroplasmic 7.7 kb mitochondrial DNA deletion. Transcripts originating from the genes located outside of the deletion were present in similar amounts to those of control samples, with the transcript levels of each tissue linked to its oxidative phosphorylation capacities. Transcripts originating from genes within the deletion were reduced according to the percentage of mtDNA deleted molecules in the tissue. The fusion transcript resulting from the rearranged genome is expressed in all the tissues tested and its level is related to the amount of the deleted mtDNA. The RNA levels from three nuclear genes encoding two of the Adenine Nucleotide Translocator isoforms (ANT1 and 2) and the beta subunit of the ATPsynthase (ATPsyn beta) were significantly induced in the different tissues independently of the percentage of deleted mtDNA molecules. In contrast, the ANT1 and ATPsyn beta levels were decreased in skeletal muscle. This result could be related to the different distribution of the deleted molecules in tissues.

Base Sequence↗
PubMed1994

OXBOX and REBOX, overlapping promoter elements of the mitochondrial F0F1-ATP synthase beta subunit gene. OXBOX/REBOX in the ATPsyn beta promoter.

Three positive (PR1-3) and one negative (NR1) transcriptional control domain have been tentatively mapped in the promoter of the human F0F1-ATP synthase beta subunit gene (ATPsyn beta) in the context of expression in myogenic cells. Lipofection of promoter-chloramphenicol acetyltransferase fusion constructs into C2C12 myogenic cells revealed that two of the three positive domains (PR1 and PR2) function in both myoblasts and myotubes, whereas the third positive domain (PR3) and the sole negative domain (NR1) seem to function only in myotubes. PR1 contains a cluster of four CCAAT cis-elements, PR2 is a small 44-base pair region containing an SP1-like motif, and PR3 is a region previously shown to be recognized by both OXBOX- and REBOX-binding factors. By site-directed polymerase chain reaction linker mutations, the activity of the OXBOX/REBOX cis-element in myoblasts is shown to be masked by flanking sequences in PR3. The negative domain, NR1, is located between 300 and 1,000 base pairs upstream from the OXBOX/REBOX elements in a region containing multiple Alu repeats. Mobility gel shift analysis of DNA-protein complexes using competitor DNAs verified the involvement of both OXBOX- and REBOX-binding factors in PR3. Similar experiments show SP1-specific binding at PR2. These data with observations of OXBOX and REBOX-specific binding of an OXBOX/REBOX-like region within the conserved sequence block C of the human mitochondrial DNA D-loop sequence are consistent with the idea that OXBOX- and REBOX DNA-binding factors coordinate the expression of mitochondrial energy genes in highly oxidative tissues by working with well characterized general transcription factors such as SP1 and CCAAT DNA-binding proteins, which exist in the nucleus, and MTF, which exists in the mitochondrion.

Animals↗
PubMed1994

Mitochondrial DNA "clock" for the Amerinds and its implications for timing their entry into North America.

Students of the time of entry of the ancestors of the Amerinds into the New World are divided into two camps, one favoring an "early" entry [more than approximately 30,000 years before the present (YBP)], the other favoring a "late" entry (less than approximately 13,000 YBP). An "intermediate" date is unlikely for geological reasons. The correlation of the appropriate data on mtDNA variation in Amerinds with linguistic, archaeological, and genetic data offers the possibility of establishing a time frame for mtDNA evolution in Amerinds. In this paper, we estimate that the separation of the Chibcha-speaking tribes of Central America from other linguistic groups/nascent tribes began approximately 8000-10,000 YBP. Characterization of the mtDNA of 110 Chibcha speakers with 14 restriction enzymes leads on the basis of their time depth to an estimated mtDNA nucleotide substitution rate for Amerinds of 0.022-0.029% per 10,000 years. As a first application of this rate, we consider the mtDNA variation observed in 18 Amerind tribes widely dispersed throughout the Americas and studied by ourselves with the same techniques, and we estimate that if the Amerinds entered the New World as a single group, that entry occurred approximately 22,000-29,000 YBP. This estimate carries a large but indeterminate error. The mtDNA data are thus at present equivocal with respect to the most likely times of entry of the Amerind into the New World mentioned above but favor the "early" entry hypothesis.

Anthropology↗
PubMed1994

Mitochondrial DNA analysis in Tibet: implications for the origin of the Tibetan population and its adaptation to high altitude.

Mitochondrial DNAs (mtDNAs) of 54 Tibetans residing at altitudes ranging from 3,000-4,500 m were amplified by polymerase chain reaction (PCR), examined by high-resolution restriction endonuclease analysis, and compared with those previously described in 10 other Asian and Siberian populations. This comparison revealed that more than 50% of Asian mtDNAs belong to a unique mtDNA lineage which is found only among Mongoloids, suggesting that this lineage most likely originated in Asia at an early stage of the human colonization of that continent. Within the Tibetan mtDNAs, sets of additional linked polymorphic sites defined seven minor lineages of related mtDNA haplotypes (haplogroups). The frequency and distribution of these haplogroups in modern Asian populations are supportive of previous genetic evidence that Tibetans, although located in southern Asia, share common ancestral origins with northern Mongoloid populations. This analysis of Tibetan mtDNAs also suggests that mtDNA mutations are unlikely to play a major role in the adaptation of Tibetans to high altitudes.

Adaptation, Physiological↗