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Alzheimer's Disease and Darwinian Evolution: Is There a Connection?

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A few years ago, a research group headed by William Seeley at the University of California, San Francisco published an intriguing report of autopsy-histology analysis of the brains of 12 patients with dementia: 5 patients with frontotemporal dementia, 7 patients with Alzheimer's disease, and 7 non-neurological control subjects. (Ann. Neurol. 2006 60:660).

Frontotemporal dementia (FTD) is a neurodegenerative dementia caused by neuron loss in various regions of the frontal and temporal lobes of the brain. FTD is usually first recognized in people in the their 60s, and of people under 65 FTD has about the same prevalence as Alzheimer's disease (AD). What the Seeley group reported was that FTD is apparently associated with degeneration of a specific type of nerve cell (von Economo neurons) unique to great apes and humans and more abundant in humans than in apes. Also, loss of these neurons occurs in FTD but not in AD. Like the frontal lobes in general, in addition to appearing late in evolution, von Economo neurons (named after the anatomist who discovered them) also mature late in development: they appear mainly after birth and achieve their maximum numbers at about 4 years of age.

The idea that neurodegenerative dementia may have something to do with evolution is not new. More than 20 years ago, Stanley Rapoport of the National Institutes of Health suggested that Alzheimer's disease is a human phylogenetic disease, and that diseases such as AD and Down syndrome involve pathological changes in the specific genes, whatever they may be, responsible for the rapid evolution of the human brain (Med. Hypoth. 1989 29:147).

More recently, only a few months ago, the Swiss neuroscientist Joseph Ghika presented a detailed analysis (including 274 references) in which he concludes that neurodegenerative diseases are age-related diseases of specific brain regions recently developed in humans via Darwinian evolution (Med. Hypoth. 2008 71:788). The general idea is that the mechanisms responsible for the rapid recent evolutionary development of the human brain are new and therefore maybe more vulnerable to disease processes than older parts of the brain. What Ghika has done is make an admirable synthesis by gathering evidence of the past several decades to amplify and extend Rapoport's old conjecture about Alzheimer's disease. Ghika makes the extension to 16 different kinds of neurodegenerative syndromes -- all related to recently evolved regions of the nervous system. In conclusion, Ghika calls for a change in the way we think of neurodegenerative diseases.

In science, we call this potentially "hot stuff" -- a new way to look at an old problem. New ways to look at old problems are among the most forceful engines to move science forward. One of the ideas floating around for many generations is that dementia diseases of old age are simply a consequence of the brain wearing out and breaking down. The idea of preventing such a breakdown seems at best daunting and at worst ridiculous. But now comes a new idea: the breakdown of mechanisms in the various neurodegenerative diseases are specific and not general -- and the idea that vulnerabilities due to rapid evolution are involved may give us specific places and mechanisms to look at.

If this new idea about neurodegenerative diseases pans out, it may make the problem of prevention more tractable. It won't happen tomorrow, but we seem to be moving forward.

P.S. I don't know what the HBO Alzheimer's documentary will tell us tonight about this new idea. I do hope they cover it.

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