Showing papers by "Douglas C. Wallace published in 1994"

Mitochondrial DNA sequence variation in human evolution and disease.

Abstract: 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.

mtDNA and the origin of Caucasians: identification of ancient Caucasian-specific haplogroups, one of which is prone to a recurrent somatic duplication in the D-loop region.

Abstract: mtDNA sequence variation was examined in 175 Caucasians from the United States and Canada by PCR amplification and high-resolution restriction-endonuclease analysis. The majority of the Caucasian mtDNAs were subsumed within four mtDNA lineages (haplogroups) defined by mutations that are rarely seen in Africans and Mongoloids. The sequence divergence of these haplogroups indicates that they arose early in Caucasian radiation and gave raise to modern European mtDNAs. Although ancient, none of these haplogroups is old enough to be compatible with a Neanderthal origin, suggesting that Homo sapiens sapiens displaced H. s. neanderthaliensis, rather than mixed with it. The mtDNAs of one of these haplogroups have a unique homoplasmic insertion between nucleotide pair (np) 573 and np 574, within the D-loop control region. This insertion makes these mtDNAs prone to a somatic mutation that duplicates a 270-bp portion of the D-loop region between np 309 and np 572. This finding suggests that certain nonpathogenic mtDNA mutations could predispose individuals to mtDNA rearrangements.

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

Abstract: 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.

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

Abstract: 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.

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

Abstract: 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. © 1994 Wiley-Liss, Inc.

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

Abstract: 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.

Mitochondrial DNA mutations in diseases of energy metabolism.

Abstract: A variety of degenerative diseases involving deficiencies in mitochondrial bioenergetics have been associated with mitochondrial DNA (mtDNA) mutations. Maternally inherited mtDNA nucleotide substitutions range from neutral polymorphisms to lethal mutations. Neutral polymorphisms are ancient, having accumulated along mtDNA lineages, and thus correlate with ethnic and geographic origin. Mildly deleterious base substitutions have also occurred along mtDNA lineages and have been associated with familial deafness and some cases of Alzheimer's Disease and Parkinson's Disease. Moderately deleterious nucleotide substitutions are more recent and cause maternally-inherited diseases such as Leber's Hereditary Optic Neuropathy (LHON) and Myoclonic Epilepsy and Ragged-Red Fiber Disease (MERRF). Severe nucleotide substitutions are generally new mutations that cause pediatric diseases such as Leigh's Syndrome and dystonia. MtDNA rearrangements also cause a variety of phenotypes. The milder rearrangements generally involve duplications and can cause maternally-inherited adult-onset diabetes and deafness. More severe rearrangements frequently involving detetions have been associated with adult-onset Chronic Progressive External Ophthalmoplegia (CPEO) and Kearns-Sayre Syndrome (KSS) or the lethal childhood disorder, Pearson's Marrow/Pancreas Syndrome. Defects in nuclear-cytoplasmic interaction have also been observed, and include an autosomal dominant mutation causing multiple muscle mtDNA deletions and a genetically complex disease resulting in the tissue depletion of mtDNAs. MtDNA nucleotide substitution and rearrangement mutations also accumulate with age in quiescent tissues. These somatic mutations appear to degrade cellular bioenergetic capacity, exacerbate inherited mitochondrial defects and contribute to tissue senescence. Thus, bioenergetic defects resulting from mtDNA mutations may be a common cause of human degenerative disease.

mtDNA and Y-chromosome polymorphisms in four Native American populations from southern Mexico.

Abstract: mtDNA sequence variation was examined in 60 Native Americans (Mixtecs from the Alta, Mixtecs from the Baja, Valley Zapotecs, and Highland Mixe) from southern Mexico by PCR amplification and high-resolution restriction endonuclease analysis Four groups of mtDNA haplotypes (haplogroups A, B, C, and D) characterize Amerind populations, but only three (haplogroups A, B, and C) were observed in these Mexican populations The comparison of their mtDNA variation with that observed in other populations from Mexico and Central America permits a clear distinction among the different Middle American tribes and raises questions about some of their linguistic affiliations The males of these population samples were also analyzed for Y-chromosome RFLPs with the probes 49a, 49f, and 12f2 This analysis suggests that certain Y-chromosome haplotypes were brought from Asia during the colonization of the Americas, and a differential gene flow was introduced into Native American populations from European males and females

Molecular basis of mitochondrial DNA disease.

Abstract: Mitochondrial ATP production via oxidative phosphorylation (OXPHOS) is essential for normal function and maintenance of human organ systems. Since OXPHOS biogenesis depends on both nuclear- and mitochondrial-encoded gene products, mutations in both genomes can result in impaired electron transport and ATP synthesis, thus causing tissue dysfunction and, ultimately, human disease. Over 30 mitochondrial DNA (mtDNA) point mutations and over 100mtDNA rearrangements have now been identified as etiological factors in human disease. Because of the unique characteristics of mtDNA genetics, genotype/phenotype associations are often complex and disease expression can be influenced by a number of factors, including the presence of nuclear modifying or susceptibility alleles. Accordingly, these mutations result in an extraordinarily broad spectrum of clinical phenotypes ranging from systemic, lethal pediatric disease to late-onset, tissue-specific neurodegenerative disorders. In spite of its complexity, an understanding of the molecular basis of mitochondrial DNA disease will be essential as the first step toward rationale and permanent curative therapy.

Mitochondrial DNA variation in human populations and implications for detection of mitochondrial DNA mutations of pathological significance

Abstract: Haplotype and phylogenetic analyses of “normal” mitochondrial DNAs (mtDNAs) have allowed a clarification of several controversial issues concerning the origin of humans, the time and colonization pattern of the various regions of the world, and the genetic relationships of modern human populations. More recently, the same type of analyses has also been applied to mtDNA disease studies. A review of these studies indicates that exhaustive screenings of “normal” mtDNA variation in all human populations associated with haplotype and phylogenetic analyses are essential if we are to understand the etiology of mitochondrial pathologies.

Mitochondrial DNA mutations in epilepsy and neurological disease.

Abstract: Summary: Recent discoveries in mitochondrial clinical genetics have revealed that a broad spectrum of clinical phenotypes are associated with mutations in mitochondrial DNA. Diseases caused by mutations in mitochondrial DNA are by nature quantitative. Myoclonic epilepsy and ragged-red fiber disease are caused by a mutation in the transfer RNA gene lysine. Although everyone in a maternal lineage will harbor the same mutation, the nature and severity of the symptoms vary markedly among individuals. This variability correlates with the inherited percentage of mutations in the individual's mitochondrial DNA and the individual's age. Age-related expression of mitochondrial disease has also been demonstrated for mitochondrial DNA deletions. Although deletions that retain both origins of replication result in late-onset disease because of the progressive enrichment of the deleted mitochondrial DNA, a 10.4-kb deletion that lacks the light-strand replication origin and maintains a stable mutant percentage in both tissues and cultured cells has been discovered. This deletion is associated with adult-onset diabetes and deafness, but not with ophthalmoplegia, ptosis, or mitochondrial myopathy. Biochemically, it causes a generalized defect in mitochondrial protein synthesis and oxidative phosphorylation. The age-related decline in oxidative phosphorylation could reflect the accumulation of somatic mitochondrial DNA mutations. Inhibition of oxidative phosphorylation stimulates this accumulation. The general paradigm for mitochondrial DNA diseases may be that inherited mutations inhibit the electron transport chain. This damages the mitochondrial DNA, further reducing oxidative phosphorylation. Ultimately, oxidative phosphorylation drops below the expression threshold of cells and tissues, and clinical symptoms appear.

Variable Retinal and Neurologic Manifestations in Patients Harboring the Mitochondrial DNA 8993 Mutation

Abstract: Objective: Ophthalmologic and neurologic manifestations of the mitochondrial DNA mutation at position 8993 ( MTATP*NARP8993 ) are reported and compared with previously published reports of patients with the 8993 mutation and other mitochondrial disorders Design: Pedigree analysis Setting: University referral center Patients: Eight subjects from two unrelated pedigrees that were positive for the mitochondrial DNA replacement mutation at nucleotide position 8993 were evaluated ophthalmologically and neurologically Results: Retinal abnormalities ranged from mild salt-and-pepper changes to severe retinitis pigmentosa—like changes with maculopathy Neurologic manifestations were also highly variable and ranged from migraine headaches to severe dementia and Leigh's disease Conclusions: The type and extent of retinal pigmentary changes and neurologic findings varied substantially, even among members of the same family These changes, although not specific for the MTATP*NARP8993 mutation, are highly suggestive of mitochondrial disease

Detection of mitochondrial DNA mutation 14459 associated with dystonia and/or Leber's hereditary optic neuropathy

Abstract: The present invention provides an assay for diagnosing or predicting a predisposition to dystonia and/or Leber's Hereditary Optic Neuropathy by detecting the presence of a mutation in mitochondrial DNA, in the oxidative phosphorylation (OXPHOS) gene ND6, that causes a substitution in amino acid 72 of the ND6 polypeptide. In particular, the mutation can be at mtDNA position 14459. Also provided are therapeutic treatments for dystonia and/or Leber's Hereditary Optic Neuropathy, as well as methods of screening compounds for effectiveness in treating these diseases and an animal model.

Mitochondrial Myopathies: Genetic Aspects

Abstract: Publisher Summary This chapter discusses the genetic aspects of mitochondrial myopathies. Mitochondria are the major producers of cellular adenosine triphosphate (ATP) by the process of oxidative phosphorylation (OXPHOS). The mitochondrial OXPHOS system encompasses five multiple subunit enzyme complexes plus the adenine nucleotide translocator (ANT), all of which are embedded in the mitochondrial inner membrane. Four of these five OXPHOS enzyme complexes contain polypeptide subunits encoded by both the nucleus and the mitochondria. The two promoters, light strand promoter (LSP) and heavy-strand promoter (HSP), of mtDNA transcription are adjacent to each other within the displacement loop (D-loop). Inverted sequences located upstream from both promoters bind mitochondrial transcription factor (mtTFl). MtTFl is required in addition to the mitochondrial RNA (mtRNA) polymerase for efficient transcription. The genetic code of the mtDNA differs from nucleus and virtually all other organisms. The mtDNA genetic code is highly degenerate, so that only 22 tRNAs are required for translation. When uridine is in the wobble position, all 4 members of a codon family can be read by 1 mitochondrial tRNA.

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

Abstract: A 40-year-old woman presented with pro found 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. © 1994 Wiley-Liss, Inc.

Recent advances in mitochondrial genetics

Abstract: Publisher Summary This chapter examines some of the recent advances in mitochondrial genetics and the way in which they have altered our understanding of rare and common age-related diseases. Normal ATP generation by oxidative phosphorylation (OXPHOS) is a complex process requiring the coordinated expression of two genomes: (1) the nuclear DNA (nDNA) and (2) the mitochondrial DNA (mtDNA). OXPHOS is carried out by five enzyme complexes assembled from subunits encoded by the mtDNA. The first four complexes (I–IV) create the electron-transport chain which oxidizes electrons from NADH or FADH 2 and uses the energy to pump protons out of the mitochondrial inner membrane. This electrochemical gradient is utilized by Complex V to synthesize ATP from ADP+P i . The ATP is then exchanged across the mitochondrial inner membrane for cytosolic ADP by the adenine nucleotide translocator (ANT). The ANT and the catalytic ATP synthase β subunit share a muscle specific cis element, the OXBOX, which results in their coordinated elevated expression in heart and skeletal muscle. In addition to the 13 OXPHOS polypeptides, the mtDNA also encodes the rRNAs and tRNAs of mitochondrial protein synthesis.