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Why do African-American women have a higher risk of obesity, while European-American
women have a higher risk of osteoporosis? As this ScienCentral News video
reports, genetics researchers are attacking these questions through the touchy
topic of race.
Disease and Ancestry
All human populations are so closely related that there are very few genes
that are different between one human and another. However, statistics seem
to show that certain races have higher rates of certain diseases.
"Black women are more prone to obesity," says Mark
Shriver, assistant professor of anthropology and genetics at Penn
State University. "There's a higher risk, about twofold, than white
women. Also, white women are more prone to osteoporosis than black women."
But there are other factors involved besides race, like differences in wealth,
power, and privilege. Geneticists at Penn State University and the University
of Alabama at Birmingham are trying to tease apart these factors, not
by ignoring race, but by studying it. They want to find out if genes important
in certain diseases are inherited with genes that make us look different.
"When the Africans came to this country and they passed genetic information to
their progeny, these sequences were the sequences that were passed on, and
we have been able to identify them," says Jose
Fernandez, assistant professor of nutrition sciences at the University
of Alabama at Birmingham. "Those sequences are different than the sequences
European people have. This battery of markers that we're using are markers
that can discriminate between, in this case, European ancestry and African
ancestry."
Shriver's lab looked at hundreds of DNA sequences called genetic markers to
estimate the percentage of genes in an individual that are Native American,
West African, or European. This information on "genetic ancestry"
can then be used to investigate the connection between an individual's ancestry
and certain diseases. "Using that then, as the variable, instead of simple
race type variables, we were able to study different traits, like obesity
and percent body fat and bone mineral density, traits that have to do with
obesity and osteoporosis," says Shriver.
Women of African ancestry have higher bone density.
The researchers looked at body
mass index, a measure of height and weight, fat mass, fat-free mass, resting
metabolic rate, and bone-mineral density, in 150 African-American women from
Birmingham, Baltimore, and New York City, and used 18 ancestry-informative
genetic markers to determine the West African ancestry proportion for the
women.
The study, which was published in the July 2003 issue of the journal Obesity
Research, revealed that there is an association between West African
ancestry and body mass index, which is a measure of obesity. But Shriver points
out, "It's important again to remember that there are lots of factors
that are going into affecting obesity risk. Most of them are not genetic.
It's expected [that] the obesity rate is going to continue rising. These are
cultural changes and sociological changes in our society. These are not genetic
changes."
The scientists say the study does show that genetic ancestry can help to focus
the search for genes that affect individuals' risks of diseases. "This
study demonstrates how we can use ancestry-informative markers to establish
the biogeographic ancestry of a sample of people," says Shriver, "and
how that can be used as an important variable in understanding the prevalence
of disease and the distribution of disease. These variables will be important
in lots of studies."
"Eventually, we would like to be able to say 'Okay, it doesn't matter
what your race is', says Fernandez. "We would like to be able to say,
'Let's look at the DNA sequences that an individual has.' We would like to
be able to say, 'Well, if you have this sequence and this sequence and this
sequence, you have a predisposition to have more body fat and that we should
try to develop an intervention strategy that is going to work with your genetic
makeup,' to avoid obesity in the population. At this point, we have to rely
on these types of studies, where the sample size is a little bit smaller."
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