The other human genome

Article Abstract:

The study of mitochondrial DNA is currently exciting a growing number of researchers. Mitochondria are small organelles in the cellular cytoplasm, in which the processes that provide cellular energy occur. They possess their own DNA, completely separate from that of the cell that houses them. It is a single, double-stranded loop, with 16,569 base pairs, and codes for only 13 proteins, for the cell's ribosomes (where all proteins are assembled), and for transfer RNAs for the mitochondria. Recent research results have linked mutations in mitochondrial DNA (mtDNA) to certain rare diseases. More common degenerative disorders, such as Parkinson's disease and Huntington's disease (both of the central nervous system) may also be associated with defective mtDNA. The mitochondrion itself is the descendant of free-living bacteria that respired (consumed oxygen and gave off carbon dioxide and water), and that were ultimately taken in by cells of higher organisms. Their number within cells varies according to the cell's energy demands: active cells have more. Their genetics, too, are unique and interesting. Mitochondria are inherited only from the mother and, when cells divide, they disperse randomly into daughter cells. Thus, a mutation may not be detectable until a large number of mitochondria have acquired it. The work of Doug Wallace, an investigator into mtDNA, is described. His focus was Leber's neuropathy, a degenerative disorder of the optic nerve. A defect in a base substitution (part of the DNA sequence) was found in nine of eleven families with this disorder. Other mtDNA diseases are those resulting from genetic deletions. These patients all have paralysis of the extraocular muscles (that move the eyes, ophthalmoplegia), as well as other symptoms. The ophthalmoplegia may be either limited, or progressive and fatal, as it is in Kearns-Sayre syndrome. Now mtDNA defects are under investigation as causative agents for a wide range of diseases, including Parkinson's disease and certain cardiomyopathies (diseases of the heart muscle). An accumulation of mtDNA mutations over a lifetime could induce cellular aging, a topic under intense investigation. (Consumer Summary produced by Reliance Medical Information, Inc.)

Physiological aspects, Genetic aspects, Mitochondria, Mitochondrial DNA, Mitochondrial myopathies

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Getting to the heart of the cholesterol debate

Article Abstract:

Recent recommendations of the National Cholesterol Education Program (NCEP) advising reductions in dietary cholesterol added fuel to the long-simmering debate over the contribution of cholesterol levels to heart disease. In spite of studies involving thousands of patients, no firm answer has emerged to the question of how strong the link is between cholesterol and heart disease. The NCEP report is based on many studies, including the Multiple Risk Factor Intervention Trial, which studied 362,000 middle-aged men and found a relationship between blood cholesterol and heart disease. An opposing viewpoint states that no correlations have been found for cholesterol levels and disease in women, children, or young men and, hence, dietary regulation would be pointless. Richard Peto is a statistician who believes that what is needed is not further research but, rather, more appropriate analysis of existing data. He has developed a type of analysis called meta-analysis, for which results from all available studies are pooled. This enables him to detect subtle patterns that are missed when smaller samples are used. Such an approach is necessary because of weaknesses in the design of many studies as well as the failure of investigators to take measurement error into account when they analyze their data. Peto also points out that cholesterol levels for people in the United States should be compared with levels for people with a low heart disease rate, such as rural Chinese. This would be used to establish a 'normal' level, against which levels for people in the United States should be measured. The scientist believes that the question of cholesterol's effects must be kept separate from the decision about whether it should be reduced. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Causes of, Statistics, Coronary heart disease, Blood cholesterol, Medical statistics, Peto, Richard

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Women left out at NIH

Article Abstract:

In recent testimony before the House Subcommittee on Health and the Environment, the National Institutes of Health (NIH) was accused of failing to live up to its own policy of increasing the participation of women in clinical trials. One major study singled out for criticism was a trial of the role of aspirin in the prevention of heart attacks. The study involved 22,000 men and not a single woman. Critics, including Patricia Schroeder of the Congressional Caucus for Women's Issues, say that American women have been put at risk by such practices; others disagree. Charles H. Hennekens, director of the study, points out that for the study population, the rate of heart attacks is three times greater among men than women. Simply adding women to the study group would not have provided any answers, and the validity of the answers obtained for the men might have been invalidated. Hennekens points out that it is important to include women and minorities in medical research, but that the inclusion should not be for political reasons, but only for scientific ones. (Consumer Summary produced by Reliance Medical Information, Inc.)

Social aspects, Investigations, Clinical trials, Science and technology policy, Medical research, United States. National Institutes of Health, editorial, Schroeder, Patricia

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