Sharon Begley has written a lovely article on Tanzi and Moir’s research on the antimicrobial properties of amyloid beta and the outrageous difficulty they have had getting NIH to fund their work. They noted that study after study has found no benefit from treatments that disrupt amyloid synthesis, and that there must be some reason why amyloid beta exists.
The crucial paragraphs are in italics below
“For years in the 1990s, Moir, too, researched beta-amyloid, especially its penchant for gunking up into plaques and “a whole bunch of things all viewed as abnormal and causing disease,” he said. “The traditional view is that amyloid-beta is a freak, that it has a propensity to form fibrils that are toxic to the brain — that it’s irredeemably bad. In the 1980s, that was a reasonable assumption.”
But something had long bothered him about the “evil amyloid” dogma. The peptide is made by all vertebrates, including frogs and lizards and snakes and fish. In most species, it’s identical to humans’, suggesting that beta-amyloid evolved at least 400 million years ago. “Anything so extensively conserved over that immense span of time must play an important physiological role,” Moir said. What, he wondered, could that be?
Their subsequent work has demonstrated beyond doubt that amyloid beta is a powerful antimicrobial  and has strongly suggested a role for herpes viruses. But despite these findings, they still are having difficulty getting their work published and getting NIH funding. I predict this will lead to a Nobel prize, and go into the history books as an especially egregious example of how pure reductionism obstructs progress. Evolutionary thinking about the reasons why we are vulnerable to Alzheimer’s disease adds the missing perspective. We can hope that it will also inspire new approaches to prevention and treatment.
- Kumar, D. K. V., Choi, S. H., Washicosky, K. J., Eimer, W. A., Tucker, S., Ghofrani, J., … others. (2016). Amyloid-β peptide protects against microbial infection in mouse and worm models of Alzheimer’s disease. Science Translational Medicine, 8(340), 340ra72–340ra72
- Eimer, W. A., Vijaya Kumar, D. K., Navalpur Shanmugam, N. K., Rodriguez, A. S., Mitchell, T., Washicosky, K. J., … Moir, R. D. (2018). Alzheimer’s Disease-Associated β-Amyloid Is Rapidly Seeded by Herpesviridae to Protect against Brain Infection. Neuron, 99(1), 56-63.e3. https://doi.org/10.1016/j.neuron.2018.06.030
Photo credit: Creator:Jon ChaseInformation extracted from IPTC Photo Metadata
The history of medicine is
replete with examples of the disasters that result when clinical practice is guided
by theory alone. For instance, in the early 20th century sudden infant
death was attributed to suffocation caused by an enlarged thymus.1 Thousands of infants received radiation
treatment that created an epidemic of thyroid cancer, with new cases still
emerging 45 years after exposure.2
Such examples make most of us in evolutionary medicine extremely
wary of basing clinical advice on theory. However, recommending aspirin to
prevent strokes and heart attacks seemed like a sure thing. In modern
environments, bleeding is less of a risk, and clots in coronary or cerebral
arteries are a much more of a risk, than in ancestral environments. Taking a
baby aspirin every day should adjust the tradeoffs to help our ancient bodies
cope better with modern environments.
Also, studies showing that a baby aspirin a day reduced heart attacks by
more than 25% led medical organizations to endorse aspirin for prevention.3
The data supported the evolutionary theory, so I started
taking a daily aspirin, and I recommended that my patients over 50 years old do
the same. Millions of people took an aspirin every day for years. But it is becoming
clear that even solid theory and supporting data are not enough.
The first warnings came from new studies showing that even small doses of aspirin caused more gastrointestinal bleeds than expected. Then, late in 2017, the results of a double-blind long-term study were published. The ARRIVE trial enrolled over 12,000 subjects averaging 55-60 years of age with an average risk for a heart attack; half got aspirin half got placebo. At the end of five years, cardiovascular death, myocardial infarction, unstable angina, stroke, or transient ischemic attack had occurred in 4.29% of the aspirin group, and 4.48% of the placebo group.4 The rate of gastrointestinal bleeding was twice as high for the aspirin group. I stopped taking aspirin and decided to write this article.
This will not be the last word on the issue; compliance was inconsistent,
and the results may not generalize to people with higher risk. Patients who
have had a cardiac event should not stop their aspirin. But the trial offers yet
more evidence that there is no substitute for a controlled trial with random assignment…and
that clinical recommendations based on apparently solid evolutionary thinking may
not be justified, even when apparently supported by data.
- Symmers D. The Cause of Sudden Death in Status Lymphaticus. Am J Dis Child. 1917 Dec 1;14(6):463–9.
- Adams (Michael) Jacob, Shore RE, Dozier A, Lipshultz SE, Schwartz RG, Constine LS, et al. Thyroid Cancer Risk 40+ Years after Irradiation for an Enlarged Thymus: An Update of the Hempelmann Cohort. Radiat Res. 2010 Dec;174(6):753–62.
- Patrono C, García Rodríguez LA, Landolfi R, Baigent C. Low-Dose Aspirin for the Prevention of Atherothrombosis. N Engl J Med. 2005 Dec 1;353(22):2373–83.
- Gaziano JM, Brotons C, Coppolecchia R, Cricelli C, Darius H, Gorelick PB, et al. Use of aspirin to reduce risk of initial vascular events in patients at moderate risk of cardiovascular disease (ARRIVE): a randomised, double-blind, placebo-controlled trial. The Lancet. 2018 Sep 22;392(10152):1036–46.
Enormous interest is being generated by a new open access article in PLoS Biology: Identifying genetic variants that affect viability in large cohorts, by Mostafavi, H., Berisa, T., Day, F. R., Perry, J. R. B., Przeworski, M., & Pickrell, J. K. The press release from Columbia was titled “Large-scale Study of Genetic Data Shows Humans Still Evolving.” New Scientist covered it as “Our genomes reveal modern-day evolution.” At The Atlantic the headline was “Huge DNA Databases Reveal the Recent Evolution of Humans.” What does the article really show?
Author summary: Our global understanding of adaptation in humans is limited to indirect statistical inferences from patterns of genetic variation, which are sensitive to past selection pressures. We introduced a method that allowed us to directly observe ongoing selection in humans by identifying genetic variants that affect survival to a given age (i.e., viability selection). We applied our approach to the GERA cohort and parents of the UK Biobank participants. We found viability effects of variants near the APOE and CHRNA3 genes, which are associated with the risk of Alzheimer disease and smoking behavior, respectively. We also tested for the joint effect of sets of genetic variants that influence quantitative traits. We uncovered an association between longer life span and genetic variants that delay puberty timing and age at first birth. We also detected detrimental effects of higher genetically predicted cholesterol levels, body mass index, risk of coronary artery disease (CAD), and risk of asthma on survival. Some of the observed effects differ between males and females, most notably those at the CHRNA3 gene and variants associated with risk of CAD and cholesterol levels. Beyond this application, our analysis shows how large biomedical data sets can be used to study natural selection in humans.
The method is creative.The authors looked at genetic data from more than 60,000+ people in the Kaiser Permanente system and 150,000+ people in the U.K. Biobank and asked if certain genetic variations were less common in older people, implying that people with those variations died young. The astounding result is that only two variations popped out. One is APOE ε4, long recognized as a cause of heart disease and Alzheimer’s disease in modern populations. The other is a variation in CHRNA3 that is associated in higher smoking rates in smokers.
- We know that about 25% of the variation in human lifespan results from genetic variations (Brooks-Wilson, 2013) so there should be genetic variations to be found. Why didn’t they show up?
- Despite having hundreds of thousands of subjects, the study was able to detect only effects from variations present in over 10% of the population. To achieve genome wide significance requires a p<10−8 Perhaps many more alleles are waiting to be identified;the authors understandably would now like to look at samples of many hundreds of thousands of people.
- Both identified alleles may qualify as “genetic quirks” that may cause harm only when interacting with modern environments.
- The authors suggest that perhaps all other common variations have been purged by natural selection, perhaps via benefits to kin from long-lived post-reproductive adults. Kin selection is powerful, but is is plausible that it would eliminate all but two common alleles that reduce fitness up at age 75? This is a better starting point than assuming that genetic drift accounts for most disease, however, it seems unlikely.
- Environments are so vastly different now from those of our ancestors that many previously neutral variations should now influence age at death.
- Mention was made about antagonistic pleiotropy and its role in aging however genes that are not polymorphic would not have any variation to find.
Brooks-Wilson, A. R. (2013). Genetics of healthy aging and longevity. Human Genetics, 132(12), 1323–1338. https://doi.org/10.1007/s00439-013-1342-z
This week’s British Medical Journal has an article “The antibiotic course has had its day,” by Llewelyn et al., that recommends against taking antibiotics for a full standard course. It goes further to challenge the WHO advice to take antibiotics “exactly as prescribed,” and suggests that cessation of symptoms is a better indicator of when to stop. This is welcome, and about time. However the bad advice doctors have given their patients for decades results from ignorance about evolutionary biology. The BMJ article does not use the word “evolution” or the phrase “natural selection.” It does not cite the work of evolutionary biologists who have analyzed this problem for years. Instead, it relies on brute empiricism. When will medicine incorporate sophisticated evolutionary biology so it can avoid making such mistakes?
The article is behind a paywall, but here are choice bits. “in materials supporting Antibiotic Awareness Week 2016 WHO advised patients to “always complete the full prescription, even if you feel better, because stopping treatment early promotes the growth of drug-resistant bacteria.” However the article goes on to say, “the idea that stopping antibiotic treatment early encourages antibiotic resistance is not supported by evidence, while taking antibiotics for longer than necessary increases the risk of resistance.” “Outside hospital, where repeated testing may not be feasible, patients might be best advised to stop treatment when they feel better, in direct contradiction of WHO advice. Of note, a recent clinical trial found that using fever resolution to guide stopping antibiotics in community acquired pneumonia halved the average duration of antibiotic treatment without affecting clinical success.”
“The fallacious belief that antibiotic courses should always be completed to minimise resistance is likely to be an important barrier to reducing unnecessary antibiotic use in clinical practice and to developing evidence to guide optimal antibiotic use. The idea is deeply embedded, and both doctors and patients currently regard failure to complete a course of antibiotics as irresponsible behaviour.”
Llewelyn, M. J., Fitzpatrick, J. M., Darwin, E., SarahTonkin-Crine, Gorton, C., Paul, J., … Walker, A. S. (2017). The antibiotic course has had its day. BMJ, 358, j3418. https://doi.org/10.1136/bmj.j3418