Dear All
New Scientist contained a very good article last month discussing just these issues (see below).
Best wishes
Dave
Under the skin
20 Apr 02
Our DNA says there 's no such thing as race. So why
do doctors still think it matters, asks Anil
Ananthaswamy
THOSE OF US who have felt a racist 's stare know that it
scalds our skin and triggers emotions ranging from
anger to shame. Last year, that anger boiled over in
race riots that rocked the US and Britain. Of course,
those riots sprang from a complex web of causes, but it
's also true that opponents on each side had one simple
thing in common : the colour of their skins.
It might seem a long way from the streets of Cincinnati
or Bradford to the hospitals and research institutes
where scientists seek to explain the diversity of human
biology. But well-meaning doctors say they, too, need
to pay attention to race. They argue that it 's a useful
indicator of people 's predisposition to disease or
response to drugs. Meanwhile, other scientists think
that this is nonsense. Geneticists know that the racial
differences most of us perceive are little more than
skin-deep. They say that medical research and
treatment based on visible racial characteristics is a
waste of time at best and downright dangerous at
worst.
Even so, the latest genetic data has added a further
twist to the argument. It turns out that you can group
people into genetically similar clusters after all -it 's
just that they don 't correspond to conventional racial
groups. But they may provide doctors with better
categories for research and treatment until the time
when diagnosis and therapy can be tailored to an
individual patient 's genes.
For most people, geneticists ' talk about the
non-existence of races runs up against the evidence of
our own eyes. The people you meet on the street are
easy to classify as being of African, South Asian,
European, or some other origin. How do we explain
these apparently clear differences between people of
different ... well, races? Don 't external features such as
skin colour, hair type, eye shape and body stature
separate us?
They do, but only on the surface. Many of these
dramatic differences are adaptations to different
climates and don 't imply any deeper genetic
differences, says Luigi Luca Cavalli-Sforza, a population
geneticist at Stanford University in California. Black
people are black because of melanin, the pigment that
protects their skin from the damage caused by strong
sunlight. White people are white because they lack
melanin, since the pigment would prevent their skin
from making enough vitamin D under the weak Sun of
high latitudes. The tall, thin stature that helps the
Masai in eastern Africa stay cool would be a
disadvantage in the Arctic where the Inuit evolved with
stout torsos and short limbs.
But while the Masai and the Inuit represent two
extremes of external appearance, in fact there are no
abrupt boundaries between human populations.
Features that appear unambiguous when you see an
individual on the street look a lot less clear-cut when
you view a wider spread of humanity. "If you walk from
Senegal to Japan and you are asked to mark a line
where the African characteristics stop and the Oriental
characteristics begin, that 's a very hard task and one
that genetics cannot help solve," says Guido Barbujani,
a geneticist at the University of Ferrara in Italy.
The notion of genetically meaningful races began to
crumble in 1972, when Richard Lewontin, a geneticist at
Harvard University, analysed variations in blood proteins
taken from populations around the world. His
conclusions came as a shock : humans from different
"races" are not as genetically different as their
appearance would suggest. He found that nearly 85 per
cent of humanity 's genetic diversity occurs among
individuals within a single population, such as the
Swedes. Another 8 per cent occurs between populations
of the same race -Swedes and Spaniards, for example.
Only 7 per cent was accounted for by consistent
differences between races. In other words, two
individuals are different because they are individuals,
not because they belong to different races.
At the time, some researchers doubted Lewontin 's
findings, pointing out that variation in proteins did not
accurately reflect variation in DNA. But nearly 25 years
later, Barbujani and his colleagues surveyed DNA
sequence diversity directly, and their results -published
in 1997 -were nearly identical to Lewontin 's. Other labs
have also replicated these results.
Lewontin and Barbujani 's research provides a way of
measuring our diversity that does not depend on our
external appearance. And it shows that as a species we
are unusually homogenous. In biology, a "race" -or
subspecies -is defined as a population that is
geographically isolated and genetically distinct from
others of the same species. To determine if a species
has races, geneticists first quantify the genetic diversity
of the species on a scale of 0 to 1. A 0 means that
individuals from different populations are no more
different than individuals from the same population,
while a 1 means that each population is made up of
genetically identical individuals, and all the genetic
differences exist between populations. For races to
exist, a species should have a genetic diversity number
of at least 0.25 to 0.3. Mammals such as coyotes,
elephants, gazelles and grey wolves have genetic
diversity numbers that range from 0.3 to 0.8, and
geneticists recognise subspecies within them. But for
humans, the number is 0.15. Compared with other
animals, we don 't meet the threshold.
Moreover, the genetic make-up of human "races"
overlaps so broadly that you can 't accurately predict
someone 's race by their genes. Barbujani and his
colleagues analysed a set of 21 DNA sequences from
1330 individuals from 32 populations worldwide. Using
the most sophisticated statistical software available,
they asked a computer to assign each individual to his
or her continent of origin. The results, to be published in
the journal Genome Research, show that the computer
couldn 't do it. With a single DNA sequence, the
computer got it wrong 80 per cent of the time. As more
sequences were added, the computer got better, but
even at its best the computer still failed 30 per cent of
the time.
So the races we think we see have little relevance to
biology. But is there a better way to get at humanity 's
underlying genetic variations? David Goldstein of
University College London thinks so. "There is quite a
simple alternative to racial labels in representing the
genetic structure," he says.
Goldstein and his colleagues analysed DNA samples
from people in eight populations from Asia, Africa and
Europe, and used statistics to sort the individuals into
genetically similar groups. They found that the people
divided into four clusters, broadly corresponding to four
geographical areas : Western Eurasia, sub-Saharan
Africa, China and New Guinea. But the clusters did not
follow established racial lines. For instance, 62 per cent
of Ethiopians were assigned to the cluster containing
most Norwegians, Ashkenazi Jews and Armenians, and
21 per cent of Afro-Caribbean individuals were grouped
alongside West Eurasians.
It 's tempting to regard these clusters as the "real"
races of humanity, but things may not be so simple.
Barbujani and his colleagues performed a similar
analysis using two entirely different sets of genetic
markers and samples from over 30 populations -a much
larger group than Goldstein 's. To their surprise, they
found that the two sets of markers yielded two different
clustering patterns, both different from Goldstein 's.
One set of markers broke people down into one largely
Eurasian group, plus two other groups in which
individuals came from all over the world. The other set
led to four groups : one made up of African and Oceanic
people, one containing Asians and native Americans,
and two other groups that were mainly Eurasian. The
differences in the two groupings are so large that
Barbujani concludes there is no obvious way of
classifying humans into a few, well-defined groups.
Goldstein, however, still believes there is an underlying
set of clusters that represent the inherent genetic
structure of humanity, and that finding it is mainly a
matter of studying the right genetic markers. "We are
all using too small a number of markers," he says. "My
guess is that when we use a large enough set of
markers and an exhaustive enough set of individuals,
the results will stabilise. In fact, I 'm quite sure that
they will."
Whatever the outcome of this dispute, one thing is clear
: conventional notions of race are -or should be -dead.
Even where doctors find race useful in predicting the risk
of certain diseases, they would do better to abandon it
in favour of the more general notion of ancestry.
Ashkenazi Jews, for instance, are prone to a rare genetic
mutation that causes breast cancer, a mutation not
shared by other white people. A focus on race can also
blind us to real groupings that cut across conventional
racial lines. Sickle-cell anaemia, for example -often
regarded as an African disease -occurs in people from all
over the world, including those from India and the
Mediterranean, because a single copy of the sickle-cell
gene protects individuals against malaria, which is
common in all those regions.
And when it comes to the more complex diseases such
as diabetes, hypertension and coronary heart disease,
the situation gets even murkier. Take hypertension, for
instance. African-Americans suffer higher rates of high
blood pressure than white Americans. But are the
underlying causes genetic, environmental,
socio-economic or a complex mixture of all three?
No one knows, says Michael Stein of the Vanderbilt
University School of Medicine in Nashville, Tennessee.
Race, when used as a proxy for our genetic make-up, is
a crude classification that glosses over the real causes
of complex diseases such as hypertension, he says. For
instance, stress -mental, physical, or financial -can
cause hypertension, and black people in the US are
more likely to suffer socio-economic stress than white
people. "By focusing on race we 've really been very
simplistic in our approach to understanding
hypertension," Stein says. "We 've done ourselves a
disservice."
Yet medical studies continue to regard race as an
important predictor of disease risk or response to drugs.
Last year, for example, Derek Exner of the University of
Calgary in Canada and his colleagues reported that a
drug called enalapril lowered blood pressure more
effectively in white patients than in black patients. The
researchers suggest that the findings may have a
genetic basis, because other studies have shown that
black and white people differ in their ability to
metabolise drugs such as enalapril. In the light of what
geneticists are saying about race, many have criticised
such studies. "All race-based biological research should
be phased out, because racial biology is an oxymoron,"
says Robert Schwartz, a former chief of the department
of haematology and oncology at the New England
Medical Center in Boston. Nevertheless, some
physicians are already claiming that enalapril should not
be prescribed to African-Americans.
Also, race-based research can reinforce stereotypes and
encourage the blaming of patients for their illnesses.
For instance, in Britain, South Asians are seen as a
"problem" population because of their higher risk of
diabetes and coronary heart disease. Medical literature
often refers to the "South Asian health problem," says
Nish Chaturvedi, an epidemiologist at the Imperial
College School of Medicine in London. "If you read that
too often, it does sound like South Asians themselves
are the problem, rather than some of the diseases that
occur," she says.
Still, some researchers maintain that races are useful
categories. "Comparing incidence rates between races
may provide some insights as to the cause of disease.
When you are thinking about allocating health resources
and developing prevention programmes, then looking at
disease by race is very important," says cancer
researcher Ray Merrill of Brigham Young University in
Provo, Utah.
There is a way to appease both camps, says Goldstein.
Genetic clusters of the sort that he and Barbujani have
identified may give doctors the hints they need, while
avoiding racial baggage. Take drug response, for
instance. Researchers normally study variations in genes
that code for drug metabolising enzymes (DMEs).
Mutations in the DMEs can affect how we process drugs,
turning a dose that is ineffectively low for one person
into a fatal overdose for another. Traditionally,
researchers have tried to correlate these variations to
race -and the traditional races do in fact differ in the
DME variations they display. But Goldstein thinks we
can do better. He argues that DME variations don 't
correspond very closely to racial categories. "We 'll see
that maybe a drug works well in a higher fraction of
individuals from one part of the world than another part,
but it 's not going to be the case that a drug works
terrifically in China and terribly in the UK," he says.
"There just aren 't those kinds of sharp differences."
In contrast, variation in six genes that code for DMEs
was strongly correlated with the four genetic clusters he
found in his latest study. "There are some cases where
the racial classification fails spectacularly," says
Goldstein. For instance, Chinese and Papua New
Guineans, who would both fall into the "Asian" racial
group, ended up in separate clusters -and their DME
variations were significantly different.
As useful as all this may be, it still falls short of the
ideal. Knowing someone 's genetic cluster still gives you
only a rough guess as to a given drug 's potency -more
accurate than if you were using racial labels, but still
not a firm prediction. "The long-term goal must be to
find the individual mutations that matter, and genotype
people," says Goldstein. "Forget about what race they
are, or even what genetic cluster they are from, just
genotype them directly and find the drug that works
best on that genotype."
But that 's still some years off. In the meantime, some
sort of ancestry-based clustering may provide the tool
medicine needs to get past the concept of race once and
for all.
Anil Ananthaswamy
Anil Ananthaswamy is a science writer in Berkeley
From New Scientist magazine, vol 174 issue 2339,
20/04/2002, page 34
Alison Macfarlane wrote:
> Another response to the same.
>
> ------- Forwarded Message Follows -------
> To: Spirit of 1848 <[log in to unmask]>
> Copies to: [log in to unmask], [log in to unmask]
> From: Paula Braveman <[log in to unmask]>
> Date sent: Thu, 09 May 2002 10:27:01 -0700
> Subject: [spiritof1848] Jack Geiger's response to Satel article
>
> [ Double-click this line for list subscription options ]
>
> Jack Geiger sent the following eloquent letter to the editor of the NY
> Times responding to Sally Satel's May 5 article.
>
> May 8, 2002
>
> To the Editor:
>
> To any competent and conscientious physician, Dr. Sally Satel's
> justification for
> being a "Racially Profiling Doctor" must seem an alarming mixture of bad
> science and bad
> medicine. Dr. Satel is determining the "race" of her patients on the basis
> of a few
> visible but superficial characteristicsskin color, facial features, hair
> texturethe product of
> a handful of genes that, in any individual, may have no association with
> other factors linked
> to disease susceptibility. Further, since there is more genetic variation
> between any two
> African Americans than there is between them and any two whites of the same
> gender, and
> vice versa, she has no basis for inventing an innate biological
> predisposition in any one of
> them. To automatically apply variations among population groups to every
> patient is to
> gamble with undertreatment, overtreatment, missed diagnoses and false
> diagnoses, and her
> staatistical count of rare black/white nucleotide variations is medically
> meaningless, since
> those may occur in junk DNA, inactive genes, or genes that have nothing to
> do with disease.
> Dr. Satel asserts that "stereotyping often works."" Well, it works
> for some cardiologists
> who project classic negative stereotypes about energy, intelligence and
> compliance onto
> some black patients, and then recommend against bypass surgery even in the
> face of urgent
> clinical indications. It works for emergency room physicians who assume
> that black
> patients seeking relief from the agony of a sickle cell crisis must be drug
> addicts looking for
> a fix. It works for physicians who surmise that a wealthy professional
> minority woman
> with abdominal pain must have gonorrhea. All these cases are amply
> documented in the
> peer-reviewed medical literature. Such spurious racial profiling and
> stereotyping are abhorrent in
> medicine, as the case of its most notorious proponent, Josef Mengele, makes
> clear.
>
> H. Jack Geiger, M.D.
> Arthur C. Logan Professor of
> Community Medicine, Emeritus
> City University of New York
> Medical School
>
> ************************
> Paula Braveman, MD, MPH
> Professor of Family and Community Medicine
> University of California, San Francisco
> 500 Parnassus Avenue, Room MU-306E
> San Francisco, California, USA 94143-0900
> telephone: 415-476-6839
> facsimile: 415-476-6051
> e-mail: [log in to unmask]
>
> [Non-text portions of this message have been removed]
>
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> __________________________________________________________________ Alison Macfarlane St Bartholomew School of Nursing and Midwifery 20 Bartholomew Close West Smithfield Tel 0207 040 5832 London EC1A 7QN Email [log in to unmask] _________________________________________________________________
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