Download Genes and Health

Genes and Health: “Choose Your Parents Carefully”
Not only do our consumption choices affect our health, but so does our initial “starting
point” as defined by our genetic structure. The aphorism about choosing your parents
carefully appears repeatedly in writing about the genetic influence of aging. While
obviously a tongue-in-cheek admonition, numerous studies show that our genetic heritage
affects our health and life expectancy in many ways. This has been demonstrated
repeatedly in laboratory experiments involving fruit flies and baker’s yeast. What is more
remarkable is that humans share the same “gene for longevity” that causes fruit flies to
live longer when that gene is selected for reproduction.
The broad connection between genetic structure and longevity carries into
numerous health-related conditions. Doctors have long known about certain populations
at risk for various diseases, such as Tay-Sachs disease (among Eastern European Jewish
populations), cystic fibrosis (common among Europeans, most common of all among
Irish people, with 1 in 19 carrying the defective gene), and sickle-cell disease (a blood
disorder common among people of sub-Saharan African descent; the disorder protects
against malaria, which is endemic in the region). Multiple sclerosis is particularly
common among people of Scandinavian descent.
Genes have been identified that increase the risk of certain types of breast cancer,
prostate cancer, and numerous other less common cancers. Hypertension and heart
disease also have strong genetic predispositions. Researchers have found an Alzheimer’s
gene, and people carrying it find it harder to remember things even when they are
apparently fully healthy. Lifestyle-affecting diseases such as restless leg syndrome and
erectile dysfunction have a genetic component. Researchers have long known that mental
illnesses have familial patterns. Now a deviant gene for serious depression has been
identified.1 More recently, using case-control methods and DNA samples, a series of
deviant genes has been linked to schizophrenia (Walsh et al., 2008). This list provides
only a small sample of known links between diseases and genetic makeup.
Almost all of this genetic understanding arose because of the huge investments
made in both public and private sectors to analyze fully the human genome, an activity
completed in 2003.2 With this information in hand, researchers increasingly find genetic
links that either increase the propensity for certain diseases (as the earlier enumeration
suggests) or in some cases specifically cause the disease (as in Huntington’s disease and
other single-gene diseases and conditions). This research has just begun; economics will
not create this research, but it will help society come to understand how best to use it.
Genetic Therapy
The same genetic information that allows diagnosis of diseases also leads to the
possibility of replacing defective genes with correctly structured ones – true “gene
therapy.” While various approaches to such therapy exist, the most common method of
introducing a replacement gene into a person with a defective gene is to alter the DNA of
a common virus (such as those that give us “a cold”). Viruses have evolved to be able to
carry packets of DNA coding and “infect” human cells with their package. When the
“infection” has been specifically tailored to replace a defective gene, the virus serves as
1
2
Depression.about.com/od/causes/a/mutantgene.htm
See www.genome.gov/10001772
the “vector” to insert the new genes into human tissue. Initial efforts at this approach
focused on single-gene diseases such as cystic fibrosis, muscular dystrophy, and sicklecell disease.
Gene therapy has just begun; most of the “successes” at this date have occurred in
laboratory animals (e.g. mice have been cured of sickle-cell disease). The promise of this
new science appears large. So also do the ethical issues associated with the technology.
The economic issues associated with this approach begin with the intellectual property
rights to individual genes (lawsuits have been filed over the issue of whether tissue
donors for basic research can claim later property rights in therapies emerging from that
research) to the obvious issues of the cost of such therapies and how our health care
system will pay for them. Chapter 15 will discuss the issues of technological change
more broadly.
Lifestyle and Genes
Lifestyle choices clearly affect our health as do genes. It may come as no surprise that
these two are also interrelated: genes affect lifestyle choices. As discussed previously,
obesity, tobacco consumption, large (but not moderate) alcohol consumption, and the use
of psychoactive drugs such as cocaine and heroin all contribute negatively to health
outcomes (both mortality and morbidity). Modern genetic analysis is now showing that
the propensity to engage in these behaviors is determined in part by genetic makeup.
For an example of this class of work, consider the “obesity gene” identified in
2007 (Frayling et al., 2007). The gene, dubbed “FTO,” is closely related to BMI.
Furthermore, the more copies one has of this particular genetic variation, the more
overweight one becomes.3 In a large European study, individuals who had inherited one
copy of the FTO averaged 1.2 kilograms more weight than those without the gene. Those
with two copies of FTO averaged 3 kilograms more. About one in six people in the
European study carried at least one FTO variant. A separate genetic variation that leads to
extreme obesity occurs in only 1 of 10,000 people.
The same “multiple-copy” issue appears in other diseases. For example, one copy
of a genetic variation increases a smoker’s risk of lung cancer by 30 percent. Two copies
increase the risk by 80 percent. The same gene predisposes individuals to nicotine
addiction.
Economic and Legal Issues Associated with Genetic Information
As information about genetic risks becomes more extensive, our society must begin to
grapple with an entire new array of economic and legal issues. First, who owns the
information, and what rights do others have to use it if they come to possess it? One can
readily envision life, disability, and health insurers seeking genetic information about
enrollees just as they now rely on health examination and questionnaire information to
help screen out poor health risks.
One can also envision employers wishing to keep people with various genetic
risks out of the workplace. While a widespread refusal to hire people with some genetic
3
For those not versed in genetics, animals (including humans) carry around hugely redundant genetic
information – multiple copies of the same gene in any DNA string. When a variant occurs, the strength of
the effect often depends closely on how many defective copies are present. This has been found in
numerous diseases and conditions, ranging from Lou Gehrig’s disease (amyotrophic lateral sclerosis) to
obesity.
risk (say, for breast cancer) might be onerous to some, in some situations such a
screening would reduce illness risk. For example, suppose one found a genetic risk that a
certain chemical used in a specific workplace caused cancers in people with a certain
genetic makeup. Would not both the employer and employee workforce be better off by
identifying in advance those with predispositions to such a chemically induced cancer
and preventing the workplace exposure?
Genetic Risk and “Sin Taxes”
Many economists (present author included) have written extensively on the economic
benefits of taxing illness-creating behaviors such as tobacco and alcohol use.4 These
behaviors are “easy” political targets for taxation because they raise great sums of money,
and if the revenue source diminishes in response to the taxation, politicians still feel good
about things because they have reduced what they view as a harmful activity.
The numerous and increasing findings of genetic links to these addictions raises a
different public policy question: Does the underlying logic for taxing these behaviors
stand up robustly when the individuals exhibiting the behavior may be genetically
“wired” to become addicted? The new era of genetic linkage to behavior and health
outcomes will likely bring this issue into a new level of debate regarding the legitimacy
of taxing people for something they are genetically predisposed to do.
4
These are not new ideas: Before the United States had an income tax, virtually the entire federal
government budget was supported by taxation on alcohol and tobacco. Indeed, the Bureau of Alcohol,
Tobacco and Firearms was formed in 1886, and became the home of “revenoors,” the widely disliked and
dreaded enforcers against home-brewed alcohol.
Genetic Risk and Optimal Insurance
A similar issue arises in the optimal design of health insurance. If a rational individual
faces an unknown risk of carrying a gene variant that causes a serious illness or death, in
some sense (if insurance markets begin to use such information either in screening for
coverage or pricing a contract), that person might wish (at a meta level) to purchase
insurance against becoming uninsurable. But insurance markets naturally seek out such
information for contract pricing. Two solutions exist to solve this dilemma: The
government can either shift to universal insurance (a topic explored in Chapter 16) or
legislate against such use of such information. The U.S. Congress did exactly that in 2008
by passing the Genetic Information Nondiscrimination Act (GINA).