American
children whose genetic roots strongly reach back to Africa are less sensitive to
insulin-a factor important in the development of type 2 diabetes-than those
whose ancestors hailed heavily from Europe.
That, according to study results in the April
issue of the journal Diabetes. Rather than relying on broad categories of race,
such as black or white, researchers in diabetes and obesity from the Keck School
of Medicine of USC and the University of Alabama at Birmingham analyzed a group
of children for 20 key genetic markers found far more often in those of African
descent than those of European descent. They found that the more African-origin
markers in children's genetic makeup, the less their bodies responded to
insulin-and the more insulin in their blood.
Rather than relying on broad categories of race, such as black or white,
researchers in diabetes and obesity from the Keck School of Medicine of USC and
the University of Alabama at Birmingham analyzed a group of children for 20 key
genetic markers found far more often in those of African descent than those of
European descent. They found that the more African-origin markers in children's
genetic makeup, the less their bodies responded to insulin-and the more insulin
in their blood.
Medical researchers have long known that diabetes disproportionately afflicts
black communities. But by using specific genetic markers of ancestry, the UAB
and Keck School team is moving beyond general concepts of race and racial
groupings to better understand how genes influence the development of disease.
"We have previously shown that African-American children are more
insulin-resistant, but prior to this study, we lacked evidence suggesting a
genetic basis of this effect," says Michael I. Goran, Ph.D., professor of
preventive medicine and physiology and biophysics at the Keck School and a study
coauthor. "With these results, we have evidence to suggest that at least part of
the different profile in African Americans may be intrinsic rather than due to
environmental factors."
"Knowing that genes may play a role in ethnic differences in risk for type 2
diabetes may influence how physicians treat their patients," adds study
co-author Barbara A. Gower, Ph.D., associate professor of nutrition sciences at
UAB. "In particular, they may want to emphasize the importance of a healthy
lifestyle to their African-American patients."
Gower indicated that follow-up analyses with individual markers will be a first
step toward identifying specific genes associated with insulin secretion or
action.
Researchers conducted their study in a group of 125 Alabama children between
ages 5 and 16 who identified themselves either as African American or European
American.
The researchers looked for 20 specific sequences of genetic code that are found
more frequently in people of African descent than in those of European descent.
This analysis measures the individuals' "African admixture," a term for the
relative proportion of their genetic make-up that reflects African origin.
Pennsylvania State University researchers came up with the genetic panel and
analyzed the DNA.
Looking at the group as a whole, the more African-origin genetic markers found
in the children, the less sensitive the children were to insulin.
Insulin works in this way: Normally, after a meal, the body breaks down
carbohydrates into glucose, or sugar, in the blood. That signals the pancreas to
secrete insulin, because insulin helps the body's cells pick up the glucose and
convert it to energy. But when cells become less sensitive to insulin, as they
gradually do in type 2 diabetes, they cannot absorb glucose as well as they
should and the sugar remains in the blood.
The proportion of African-origin markers found in the children also was linked
to higher fasting insulin (levels of insulin in the blood between meals) and
greater acute insulin response (levels of insulin in response to glucose from
food).
Socioeconomic status, meanwhile, only was related to acute insulin response. The
lower the socioeconomic level of children's families, the greater the acute
insulin response.
Researchers say the study suggests that genetic factors may influence the
pancreas' function, the ability of the liver to get rid of insulin, or both.
Because social and environmental factors also appear to play a role, though,
identifying the specific factors at fault also will be important in
understanding and preventing the racial and ethnic disparities seen in type 2
diabetes.
In the future, the team hopes to use additional genetic markers to better
characterize people's genetic makeup and eventually track down the specific
genes that are associated with insulin sensitivity and acute insulin response.
Source: Diabetes In Control Dot Com: Diabetes,April 2003.
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