Predictive Human Genomics Is Here

Thanks to breakthroughs in genomics testing, physicians now have tools for true preventive medicine. Gene chips and genomics test panels can predict one’s predisposition towards many serious -- and often preventable -- genetic diseases and allow doctors to modify gene expression through precise, targeted, individualized interventions.

The monumental accomplishment of decoding the human genome is nearly complete. The results of work of the official government-sponsored Human Genome Project together with the efforts of private firms such as Celera and Human Genome Sciences has created a true inflection point in the curve of medical history. The human genome, arguably The Rosetta Stone of the human body, is presently undergoing intense scrutiny by scientists in nearly every country in the world. The potential benefits of these efforts for improving human health and well-being are incalculable.

"The greatest payoff from understanding the human genome is likely to be an illumination of the molecular pathogenesis of disorders that are currently poorly understood and for which treatments are …frequently sub-optimal….Genomics offers … the greatest opportunity for development of targeted therapy since the development of antibiotics,"¹ according to Frank S. Collins, M.D., Ph.D. of the National Human Genome Research Institute, National Institutes of Health, Bethesda, Md.

Historically, previous medical disciplines have dealt largely with the after-effects of an individual's genetic inheritance. Genomics and these other new disciplines, on the other hand, look directly at the genes themselves. They look at an individual's genetically programmed biochemical pathways of life under conditions of health and disease. For the first time ever, physicians have the tools to help their patients employ truly preventive medicine. Genomics may help scientists find ways of modifying human biochemistry long before a genetically predisposed disease has a chance to appear.²

Rifling through the dusty pages of medical history, however, it seems axiomatic that our powers for diagnosing diseases has preceded our ability to offer effective treatment for them. This also seems true on the new genomics frontier as well.

Testing for genetic diseases

Enter predictive genomics, the identification of the genetic predisposition of individuals to certain diseases, which is the diagnostic arm of the new genetics-based paradigm. This field has already advanced to the point that a number of sophisticated diagnostic tests are currently available to help predict one's predisposition towards many serious (although preventable or modifiable) genetic diseases.

The fact that proteomics and other therapeutic modalities are still in their infancy is in keeping with the historical diagnostics-first-therapeutics-later tradition. Progress in the sister specialties of proteomics, bioinformatics, and systems biology should eventually provide ever more effective therapeutic modalities for patients with these genetic predispositions in the years ahead.

Roger Williams, M.D. in the 1950's, introduced the concept of biochemical individuality: that every individual possesses a specific and unique biochemical blueprint.³ Until a few years ago, however, discovering what constitutes our biochemical individuality has been hit-and-miss at best, the empiric result of decades of careful trial and error.

For example, after many years of observation, one person may have noticed that he has more energy when eating protein for breakfast, that eating strawberries gives him a rash, and that he gets a headache if he consumes artificial sweeteners. Yet, another person feels sluggish if he has too much protein for breakfast, but seems to have no problems with strawberries or artificial sweeteners. Truly, "One man's meat is another man's poison," for we are all biochemically unique.

As a direct result of data from The Human Genome Project, however, we have begun to obtain much more information regarding our biochemical individuality in a rapid, quantifiable and affordable fashion. The tools of modern science can now accomplish in minutes what once took years of trial and error. One company, Orchid Diagnostics, currently offers products and services to help physicians and laboratories perform HLA genotyping (to assist with matching of donor transplant organs with recipients), disease susceptibility testing and immunogenetics. Each of their systems is capable of performing over 500,000 genotype analyses per day.⁴

Genomics testing may soon be able to predict precisely what foods are best for us, prescribe individualized exercise and other lifestyle prescriptions, and recommend a personalized list of supplements, neutraceuticals, and prescription drugs for maximum health and disease avoidance. This will all be based on an examination of our personal genetic makeup.

One often hears of life being compared to a game of cards. An individual born with a serious genetic disease such as Cystic Fibrosis or Huntington's Disease is thought of having been dealt a "bad hand." Conversely, the 105-year old we read about who attributes her longevity to "Eating a jelly donut for breakfast and smoking two packs of cigarettes every day" would clearly seem to have started life with exceptionally good cards.

The Mendelian concept of "genetic determinism" - that the genes with which we are born will determine our fate in an absolute fashion - has given way to a newer hypothesis of "genomic relativism." Genes don't determine what diseases we will acquire, they merely predispose us to them. The implications of this simple concept for the future of healthcare and preventive medicine are far-reaching.

While there are a few genes that do condemn an individual to an almost certain fate (such as the Cystic Fibrosis or Huntington's Chorea genes mentioned above), these constitute only a tiny fraction of the 35,000 or so genes that comprise the entirety of the human genome. The overwhelming majority of the time, our genes merely predispose us to disease conditions that will either manifest or not later in life depending on the lifestyle choices we made earlier on. We end up reaping later in life what we ourselves sowed in our youth.

Continuing with our gaming analogy, the cards we are dealt represent our genetic heritage. We call this sum total of our genetic makeup, the totality of our inherited DNA, our "genotype."

Our genetic heritage (our starting hand) expresses itself throughout the course of our lifetimes as a consequence of the environment in which we live and the lifestyle choices that we make (how well we play). Like any good card game, it is this combination of luck (genetic makeup) plus skill (lifestyle choices and environmental factors) that makes for an exciting outcome. This concept of genomic relativism is at once enabling and terrifying. The age-old of battle of predestination vs. free will is being fought on the front lines of our nuclear DNA. And it is now looking like very little about our future health is absolutely predestined or predetermined.

Doctors now realize that almost all human diseases result from the interaction of genetic susceptibility with modifiable environmental factors. In the overwhelming majority of cases, genetic variations do not cause disease; rather, they influence a person's susceptibility to disease as a result of lifestyle choices and environmental factors. It's not "nature" vs. "nurture," but nature (genetic heritage) and nurture (lifestyle/ environment).

Compared with looking at one's "genotype," it's more compelling to watch how the genetic code is translated, i.e., the "phenotype" of one's genetic expression, particularly the subtle differences between individuals. More than 99% of human DNA is identical among all people. Yet, it is this fraction of one percent that is different that creates all the variety of life and ensures that no two humans (other than identical twins who have precisely the same DNA) will be exactly alike.

This fraction of a percent difference in DNA from person to person is of critical importance. In the course of replicating itself billions and trillions of times, as it must do to create all the cells and tissues of the body, our DNA undergoes numerous opportunities for errors. These mistakes or imperfections in our DNA most commonly take the form of what are called point mutations, deletions or translocations. These variations are collectively known as "polymorphisms" (literally, multiple shapes). Our biochemical individuality derives largely from these polymorphisms, 100,000 or so of which have been found to date.

Specific genetic polymorphisms that involve only a single nucleotide (DNA subunit -- cytosine, thymine, adenine, or guanine) are the most common variant, and such "single nucleotide polymorphisms" (SNPs, pronounced "snips") are extremely common in the population at large. It is estimated that 50% of people have at least one of the known SNPs.

By convention, rare single-nucleotide imperfections in the genetic code are referred to as mutations. When a specific mutation is so common that it affects more than 1% of the population, it is called a polymorphism or SNP. These polymorphisms are important because they can change the manner in which the body functions, and, in some cases, predispose us (or make us more resistant) to specific diseases.

Individualized healthcare

It is axiomatic of the new theory of genomic relativism that just because we have a genetic variation that predisposes us to a certain disease, say heart disease, breast cancer, rheumatoid arthritis or osteoporosis, it does not mean that we are predestined to get that disease some day. The fundamental equation of predictive genomics is:

Genetic predisposition + environment + modifiable lifestyle choices = phenotypic expression

Predictive genomics testing signals the beginning of truly individualized healthcare. Physicians can now begin to evaluate each patient's unique genetic predispositions and then develop and implement a carefully targeted, customized plan for intervention years before pre-disease imbalances or disease symptoms begin to appear.

Almost all of the most common disabling and deadly degenerative diseases of our time, including cardiovascular disease, cancer, Alzheimer's Disease and adult-onset diabetes,⁸ are thought to be the result of interaction between genetic and environmental factors.

With clinical insight such as this, physicians will gain a deeper understanding of disease processes and be able to develop more rapid and efficacious interventions.

Predictive genomics attempts to identify the most significant single nucleotide polymorphisms (SNPs) in individuals. This is done to predict the likelihood that an individual is predisposed to develop a particular chronic disease or functional imbalance and evaluate the risk that this disease or imbalance might appear under circumstances of particular environmental or lifestyle choices.

Predictive genomics may make medical practice in the near future radically different from the medicine of today. Just as individuals will no longer be forced to play the poker game of life blindfolded, neither will their doctors. Rather than having to guess what lifestyle choices to make, individuals may finally get to look at the owner's manual for their particular bodies. Instead of relying on randomized studies involving large patient populations, doctors will have access to sophisticated diagnostic and therapeutic tools individualized for each of their patients.

We may find such freedom enabling, but terrifying as well. The scary part will be that individuals will be required to take ever-greater personal responsibility for maintaining their own health and longevity. The more powerful and dangerous the genetic idiosyncrasies with which an individual is born, the greater the responsibility on that individual to modify their environment, diet and lifestyle to attenuate the expression of that potentially harmful genetic material. As a result, physicians will move laterally into positions as co-workers or counselors with their patients, rather than as paternalistic "medicine men" or even "healers" who possess and dispense wondrous "cures."

The same SNP that can be harmful to an individual in one environment can be beneficial to that same individual under different circumstances. For example, a SNP that has historically afforded individuals a better chance of survival during periods of famine or near starvation may render those persons significantly more prone to obesity under conditions of excess or even adequate calories. The nearly ubiquitous incidence of obesity among modern day Pima Indians is testimony to the variegated expression of the same genetic mutation under different environmental circumstances.⁶

The power of predictive genomics to alter medical practice and allow physicians to practice true preventive medicine seems awesome. However, despite the signs in the road warning of "Wonders Ahead," I predict that only a small percentage of patients who might be helped by predictive genomics testing will take advantage of its availability within the next few years.

The inherent conservatism of the medical community as well as the intrinsic reluctance of the population at large to accept dramatic changes in their worldview will force a delay in popular implementation of this paradigm shift. Most physicians and patients will be likely to continue wandering in the barren but familiar landscape of the prehistoric genetic desert for a number of years before arriving at The Promised Land of Predictive Genomics.

The groups most likely to avail themselves more quickly of the new diagnostic information emanating from Predictive Genomics testing will include:

I predict that this radical shift in medical diagnostics will take several years to filter throughout the medical community and enter common usage among the general populace. For widespread acceptance to occur, physicians and patients alike will be forced to take giant strides in their conceptualizations of why we get sick. The very idea that patients can be tested before the fact for the diseases to which they are predisposed represents a very big first step.

Taking it to the next level and realizing that patients themselves are largely responsible for their own fates may take an even greater stretch of the imagination. It will definitely represent a major paradigm shift in thinking for patients and physicians alike. Such a drastic alteration in our concept of health and disease--that we are each largely responsible for our destiny--will make many folks very uncomfortable indeed.

Testing panels

At this time (mid-2002), several genomics testing panels are commercially available. Each of these panels tests for a dozen or so SNPs at a cost of a few hundred dollars per panel. Within a few years, thanks to the Law of Accelerating Returns,⁷ for the same few hundreds of dollars, panels will be available that test for thousands of genetic predispositions.

We will also soon have access to "DNA chips" that will test for most, if not all, of the 100,000 or so SNPs currently identified.⁸ ⁹ One company, Affymetrix, is currently making gene chips available to doctors for analyzing our DNA and tracking gene expression in tumors and other tissue they are sufficiently optimistic about their prospects that their toll-free number is (800) DNA-CHIP. Affymetrix and other companies have developed silicon-coated glass wafers that can be subdivided into over 150,000 distinct locations, so we will be able to detect polymorphisms on tens of thousands of genes in a matter of minutes.

The road to these "DNA chips" may have a few hurdles to cross first, at least before this information is available at low cost. It seems that a few years ago, the overwhelming majority of information found in DNA didn't seem to bear any relationship to the genes themselves and came to be known as "junk DNA." Researchers have since learned that these "non-coding" regions of the DNA are not "junk" at all, but contain vital information. Many SNPs, in fact, are found in these non-coding DNA segments.¹⁰

A small Australian biotech company called Genetic Technologies of Melbourne was among the first to realize that SNPs found outside of the genes themselves may be just as important as genetic polymorphisms themselves and registered a number of patents in the 1990's relating to this discovery. Genetic Technologies currently seems dedicated to cashing in on these patents and has threatened to sue companies who try to use this information without first paying large royalties.¹¹

Without discussing the legality or morality of such operations, genomic testing could easily end up be much more costly as a result of these and similar patents and lawsuits. With our current knowledge and abilities, however, even if the massive amounts of data that could be found on DNA chips were available, it would likely produce little beyond information overload. We need to wait for the bioinformatics scientists to catch up.

At the present time, because of both the cost considerations and our limited abilities to make meaningful sense of the data, today's clinicians need to apply limiting criteria to determine which polymorphisms it makes most sense to screen. In so doing, we can establish which SNPs should be included as part of a comprehensive preventive health program that incorporates predictive genomic testing. Presently, the numbers seem quite manageable.

Of the 100,000 SNPs currently identified, only 8,000 seem relevant to health. These 8,000 polymorphisms are relevant because they exert a significant effect on our biochemistry and physiology. Frankly, we don't know what the other 92,000 do … at least not yet.

Given our current knowledge of the human genome, only polymorphisms that exist in a significant percentage of the population are likely to be identified and evaluated in a cost-effective manner. Polymorphisms of sufficient prevalence among the population at large slice the pool down to about 300 SNPs.

It seems both prudent and ethical to test primarily for polymorphisms whose effects are modifiable through the use of currently available interventions. Finding out that a patient has a genetic defect that cannot be modified by any presently available therapy may create as much anxiety as good (although patients should have the right to know if they wish). About 100 SNPs are currently modifiable through interventions such as diet, lifestyle, nutritional supplements, and prescription pharmaceuticals.

In an ideal situation, the effects of our interventions should be easily measurable through presently available functional laboratory testing. In the year 2002, this brings the total of relevant, prevalent, modifiable and measurable genetic polymorphisms down to the easily manageable number of a few dozen or so.

Genomic test panels

The more common of these single nucleotide polymorphisms have been assembled into genomic test panels. Currently, four predictive genomic panels are commercially available for physician use:¹² a cardiac risk panel, an osteoporosis risk panel, an immune function panel and a detoxification panel.

The Cardiovascular Risk Panel identifies genetic single nucleotide polymorphisms associated with increased risk of developing coronary artery disease, other vascular diseases, Alzheimer's Disease, and hypertension. Risk factors measured include markers for inflammation, folic acid defects, iron storage problems, blood coagulation abnormalities, and cholesterol regulation defects, as well as cardio-protective markers. The information from such profiling will provide the ability to predict heart disease decades before symptoms appear.¹³

The Osteoporosis Risk Panel identifies SNPs associated with increased risk of developing bone loss. Risk factors include defects in calcium and vitamin D metabolism, parathyroid hormone action, abnormal collagen synthesis, and chronic inflammation.

The Immune Panel identifies SNPs associated with increased risk of developing immune dysfunction. Risk factors include altered production and activity of cytokines such as interleukins and Tissue Necrosis Factor-alpha (TNF-a) that may lead to inflammation and altered immunity. These SNPs have been associated with increased risk of asthma, rheumatoid arthritis, some types of cancers and other diseases.

The Detoxification Panel identifies SNPs associated with increased risk of developing detoxification defects, especially with increased exposure to environmental and other toxins. Risk factors include altered liver detoxification processes, including defects in glutathione conjugation (the detoxifier molecule mentioned in the sidebar below). Defects in the body's detoxification pathways have been associated with increased risk for certain cancers, chronic fatigue, multiple chemical sensitivity, and alcoholism.

Some patients may feel it worthwhile to screen with all four panels, while others may prefer to pick and choose one or more of the panels they feel are most relevant to them.

The testing procedure itself is very simple. Cells are collected either by using a mouth rinse solution collected at the patient's home or from a simple blood draw in the physician's office.

Many patients are understandably concerned about the confidentiality of their genomics testing results. Manufacturers of the genomics test panels have made the sage decision to address these issues before problems occur and have concluded that genomics test results require a higher level of security and confidentiality than other test results. At the testing facility, genomics testing results are protected by a security code that is disclosed only to the patient's attending physician.¹⁴

It would be tragic for genomics test results to be used by agencies such as insurance companies and HMOs to discriminate unfairly against individuals who have been proactive in seeking to achieve better health. So in most medical offices, copies of genomics test results are not included with the patient's regular medical records, but are kept in a separate secure location. This is done to ensure that such information is not routinely available to insurance companies who do not yet have sufficient experience with genomics testing to understand the full implications of these results.

Just as I was preparing to finish this article (in fact, I had only these concluding paragraphs to complete), I got the results of my own genomics profile back from the lab. As is often the case where hopes and dreams in life collide with reality, the outcome of my tests was less ideal than I had hoped, but not as bad as I had feared. I found out that I am among the 30% of the population who carries the Apo E4 gene. While I haven't lost sleep over this information, I have found these results disturbing. This information has introduced a light chop onto the calm waters of my inner tranquility.

Luckily, though, I have the more common and less risky E3/E4 genotype, not the distinctly more malevolent E4/E4. Yet, I now live with the knowledge that my chances of developing Alzheimer's Disease at some point in my life are 2-3 times average. From a purely statistical point of view, the chance that a man my age with the E3/E4 genotype will develop AD within the next 30 years is 14%.

All things considered, I am still glad I took this test. I found I had other genetic risk factors as well. Now knowing precisely what some of these risks are has stimulated me to be even more vigilant in my health maintenance efforts. To help reduce my chance of developing Alzheimer's Disease and some other diseases for which I find I am at above average risk, I plan to reduce my consumption of saturated fat significantly. I plan to eat more fish. I will also make some modifications to the nutritional supplements I take.

But, knowing that all of the genetic risks that have been identified for me are just that -- risks and not diseases -- gives me hope, and also tools to keep some of these dreaded maladies at bay. So, I am very glad that I took this test.

Genetic engineering disciplines

As a direct outgrowth of the Human Genome Project, a number of new scientific disciplines have been created to help interpret and capitalize on the voluminous amounts of data that is being generated each day.

Genomics testing for cardiovascular conditions

I want to offer one practical example of the type of information available through genomics testing. We will examine one specific marker that is part of the Cardiovascular Genomics Profile -- the apolipoprotein E (Apo E) polymorphisms. We will first discuss the specific risks and benefits associated with the different Apo E polymorphisms. Then, we will discuss how this information can result in lifestyle recommendations, which can help an individual modify the phenotypic expression of the more dangerous genotypes.

Apolipoproteins are carrier proteins responsible for the transport of lipids such as fat and cholesterol throughout the bloodstream. Since fat and cholesterol are oily substances that are not water-soluble, they require specific carrier molecules to help move them from place to place in the body.

One important lipid carrier protein, Apolipoprotein E, comes in three main polymorphic flavors -- Apo E2, Apo E3 and Apo E4. These three lipoproteins differ in the amino acids found at locations 112 and 158. Apo E2 has the amino acid cysteine at each of these loci, while Apo E4 substitutes arginine in each location. The most common type, Apo E3, has one of each, cysteine at site 112 and arginine at site 158.¹⁷ These subtle differences produce significant variations in how Apo E performs its duties of pick up and delivery of lipid bundles. One isoform, Apo E2, performs its job of clearing cholesterol from the arteries quite well, while Apo E4 is much less efficient.

Every person possesses two copies of the Apo E gene, one inherited from each parent. There are, thus, six possible combinations: E2/E2, E3/E3, E4/E4, E2/E3, E2/E4 and E3/E4.

It is known that individuals who possess one or two copies of the E4 polymorphism have an increased incidence of elevated cholesterol, triglycerides and coronary heart disease.¹⁸ Of even greater clinical significance, however, is the correlation between the presence of Apo E4 and the incidence of Alzheimer's Disease (AD). The effect of this polymorphism on AD is actually quite dramatic.

Individuals who do not have any copies of the Apo E4 allele have only a 9% risk of developing AD by age 85. People with one copy of the gene (the E3/E4 genotype carried by over 25% of the population) have a 27% chance that they will develop AD by the same age. For individuals who possess two copies (E4/E4), the risk of developing Alzheimer's increases to 55% by the age of 80.¹⁹

Furthermore, the age at which dementia is diagnosed is much younger, depending on the number of copies of Apo E4 carried: 84 years old if one has no copies of E4, 75 years if one copy and a mean age of 68 years in E4/E4 homozygotes.²⁰

Pathological examination of brain tissue of Alzheimer's patients reveals three main types of abnormalities: extracellular amyloid plaques, intracellular neurofibrillary tangles, and vascular amyloid deposits. It is probably no coincidence that Apo E4 has been immunochemically linked to each of these types of deposits.

The Apo E2 gene, on the other hand, appears to confer some degree of protection against development of AD, and patients with at least one copy of the E2 allele have a 40-50% reduction in their Alzheimer's risk.²¹ Apo E2 is not perfect, however, as some forms of heart disease are more common in patients with this polymorphism. All things considered, Apo E2 is a pretty good deal, however, and it is not unlikely that our 105 year-old smoker mentioned above was born with one or two copies of Apo E2. The Apo E3 form is the most common, by far, (over 50% of the population is E3/E3) and affords some protection against both heart disease and Alzheimer's.

In a large study of 12,709 male twins who were 62-73 years old, the odds of developing AD was 17.7 for genotype E4/E4 versus E3/E3 (i.e., an almost 18-fold increased risk) and 13.8 for E4/E4 versus all remaining genotypes. By contrast, the odds ratio for heterozygous E3/E4 was only 2.76 versus E3/E3 and 2.01 versus all other genotypes.²²

Although the Apo E4 allele is a potent risk factor for AD and may be associated with other forms of dementia, the good news is that most people who carry the Apo E4 gene still do not develop dementia, and about one-half of people diagnosed with AD do not possess any copies of the Apo E4 gene.²³ In some studies, it has been reported that the proportion of patients with dementia that is attributable to the Apo E4 allele is estimated to be only 20%.²⁴

Free radical damage appears to play a key role in the creation of insoluble beta-amyloid, one of the hallmarks of AD pathophysiology. Therefore, particularly for individuals who discover they carry the Apo E4 gene, special efforts to limit free radical damage seem prudent.²⁵ Patients who have been identified as Apo E4 carriers would be advised to begin taking aggressive free radical damage control measures, i.e., anti-oxidant and other therapies, as early in life as possible.

The following practical recommendations are suggested for patients carrying the Apo E4 genotype (although they could also be of value for anyone):

¹ Collins, FS, Guttmacher AE. Genetics moves into the medical mainstream. JAMA. 2001 Nov 14;286(18):2322-4
² Flower J, Dreifus LS, Bove AA, Weintraub WS. Technological Advances and the Next 50 Years of Cardiology. J Amer Coll Cardiol, 35:(4):1082-1091.
³ Williams, Roger J. Biochemical Individuality : The Basis for the Genetotrophic Concept. New York: Keats, 1998.
⁴ http://www.orchid.com/products/lsg/products/uht.asp
⁵ http://www.genovations.com/overview.html
⁶ Coleman DL. Diabetes and obesity: thrifty mutants? Nutr Rev 1978 May;36(5):129-32.
⁷ Kurzweil, Ray. The Age of Spiritual Machines. New York: Viking, 1999, p.30.
⁸ Francis Collins, American College of Cardiology Annual Scientific Session, New Orleans, March 1999.
⁹ Wu, Corinna. "The Incredible Shrinking Laboratory," Science News, 15 (8/15/98): 154, pp 104.
¹⁰ Roth FP, Hughes JD, Estep PW, Church GM. Finding DNA regulatory motifs within unaligned noncoding sequences clustered by whole-genome mRNA quantitation Nature Biotechnology 1998; 16: 939-45.
¹¹ http://www.newscientist.com/news/print.jsp?id=ns99992280
¹² These tests are available through Great Smokies Diagnostics Laboratory www.gsdl.com.
¹³ "Genomic Medicine and Novel Molecular Therapies in Cardiovascular Medicine," Victor Dzau, Bishop Lecture, American College of Cardiology Annual Scientific Session, New Orleans, March 1999.
¹⁴ http://www.genovations.com/patient_privacy.html
¹⁵ Bickeboller H, et al. Apolipoprotein E and Alzheimer disease: genotype-specific risks by age and sex. Am J Hum Genet 1997 Feb;60(2):439-46.
¹⁶ Additional contact information for Great Smokies Diagnostic Laboratory/Genovations™ is 63 Zillicoa Street; Asheville, NC 28801 Ph: 1-800-522-4762 (8AM - 8PM EST) ; Fax: 1-828-252-9303 ; e-mail: cs@gsdl.com.
¹⁷ This is an oversimplification. For all of the many Apo E amino acid substations possible, please visit the National Library of Medicine website:
http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?107741#MAPPING
¹⁸ Eto M, et al. Familial hypercholesterolemia and apolipoprotein E4. Atherosclerosis 1988 Aug; 72(2-3):123-8.
¹⁹ Myers RH, Schaefer EJ, Wilson PW, D'Agostino R, Ordovas JM, Espino A, Au R, White RF, Knoefel JE, Cobb JL, McNulty KA, Beiser A, Wolf PA. Apolipoprotein E epsilon4 association with dementia in a population-based study: The Framingham study. Neurology 1996 Mar;46(3):673-7
²⁰ Kamboh MI. Apolipoprotein E polymorphism and susceptibility to Alzheimer's disease. Hum Biol 1995 Apr; 67(2):195-215.
²¹ Farrer LA, Cupples LA, Haines JL, Hyman B, Kukull WA, Mayeux R, Myers RH, Pericak-Vance MA, Risch N, van Duijn CM. Effects of age, sex, and ethnicity on the association between apolipoprotein E genotype and Alzheimer disease. A meta-analysis. APOE and Alzheimer Disease Meta Analysis Consortium. JAMA 1997 Oct 22-29;278(16):1349-56
²² Breitner JC, Jarvik GP, Plassman BL, Saunders AM, Welsh KA. Risk of Alzheimer disease with the epsilon4 allele for apolipoprotein E in a population-based study of men aged 62-73 years. Alzheimer Dis Assoc Disord 1998 Mar;12(1):40-4.
²³ Myers RH, Schaefer EJ, Wilson PW, D'Agostino R, Ordovas JM, Espino A, Au R, White RF, Knoefel JE, Cobb JL, McNulty KA, Beiser A, Wolf PA. Apolipoprotein E epsilon4 association with dementia in a population-based study: The Framingham study. Neurology 1996 Mar;46(3):673-7.
²⁴ Slooter AJ, Cruts M, Kalmijn S, Hofman A, Breteler MM, Van Broeckhoven C, van Duijn CM. Risk estimates of dementia by apolipoprotein E genotypes from a population-based incidence study: the Rotterdam Study. Arch Neurol 1998 Jul;55(7):964-8.
²⁵ Retz W et al. Free radicals in Alzheimer's disease. J Neural Transm Suppl 1998;54:221-36.
²⁶ Rosler M, et al. Free radicals in Alzheimer's dementia: currently available therapeutic strategies. J Neural Transm Suppl 1998;54:211-9.
²⁷ Pasinetti GM. Cyclooxygenase and inflammation in Alzheimer's disease: experimental approaches and clinical interventions. J Neurosci Res 1998 Oct 1;54(1):1-6.
²⁸ Engel RR, et al. Double-blind cross-over study of phosphatidylserine vs. placebo in patients with and without apolipoprotein E4. Atherosclerosis. 1990 Sep;84(1):49-53.
with early dementia of the Alzheimer type. Eur Neuropsychopharmacol 1992 Jun;2(2):149-55
²⁹ Khalsa, Dharma Singh and Stauth, C. Brain Longevity. New York: Warner Books, 1997.
³⁰ Fletcher GF.The antiatherosclerotic effect of exercise and development of an exercise prescription. Cardiology Clinics 1996; 14 (1): 85-95.