Gene
Finding Lends Clues to Blood Pressure Problems
A new genetic discovery may help explain why some
people develop high blood pressure and others do not, and why some
people's blood pressure increases as they age, according to a report
in the American Journal of Hypertension.
The findings also give new insight into how the
kidneys govern the balance of salt in the body, a crucial task for
regulating blood pressure.
And, it reveals how a gene already linked to behavior
and mental health can play a role in the body, as well as the brain.
The researchers say that one in four adults in the
US has high blood pressure, also called hypertension - and many do
not know it.
If high blood pressure is not lowered with the help
of diet, exercise, and medication, it can dramatically raise the risk
of heart attack, stroke, or kidney problems.
Blood pressure, measured with a blood pressure cuff
and stethoscope by a nurse or other healthcare provider, is the force
of the blood pushing against the artery walls. Each time the heart
beats, it pumps blood into the arteries, resulting in the highest blood
pressure as the heart contracts.
Two numbers are recorded when measuring blood pressure.
The higher number, or systolic pressure, refers to the pressure inside
the artery when the heart contracts and pumps blood through the body.
The lower number, or diastolic pressure, refers
to the pressure inside the artery when the heart is at rest and is
filling with blood.
Both the
systolic and diastolic pressures are recorded as "mm Hg" (millimeters
of mercury). This recording represents how high the mercury column
is raised by the pressure of the blood.
Individuals are considered to have high blood pressure
if their blood pressure is greater than 140 mm Hg systolic, or 90 mm
Hg diastolic.
The researchers report that in the study, blood
pressure was higher and more likely to rise with age among persons
who had an extra-long form of a gene called DRD4.
They made the discovery by studying the genes of
864 people from 286 families taking part in a long-term blood pressure
genetics study called GenNet.
The families all live in or near the town of Tecumseh,
Mich., which since 1958 has been home to a U-M clinical research initiative
called the Tecumseh Community Health Study.
The finding of a link between DRD4 and blood pressure
came as a surprise to researchers who tested this gene initially to
look at genetics and behavior.
Cells use the DRD4 gene to make a receptor for a
chemical called dopamine, which transmits messages between cells.
Dopamine is best known for its role in the brain,
where it is involved in feelings of pleasure, and in governing movement.
Some studies have suggested that variations in genes
for dopamine receptors are linked to certain behavioral traits or personality
types.
But in recent years dopamine has also been found
to play a role in regulating the release of salt by the kidneys. The
new finding adds more evidence for that role.
"While many genes are involved in blood pressure
and the inherited risk of developing hypertension, we're learning that
variations in genes for dopamine receptors play a significant role," says
senior author Dr. Alan Weder, professor of internal medicine at the
University of Michigan Medical School.
"As we learn more, we may be able to determine which
patients need the most aggressive blood pressure treatment, and to
develop drugs that can lower blood pressure by intervening directly
in the proximal tubules of the kidneys, where dopamine acts - something
today's drugs don't do," Dr. Weder explains.
The new study is the first to show that the DRD4
receptor plays a role in the regulation of blood pressure by the kidneys,
and to show that a common variation in the gene is associated with
higher blood pressure.
Two other dopamine receptors have previously been
shown to be linked to blood pressure regulation.
Blood pressure, especially the systolic pressure,
tends to rise as a person gets older. And in older people, high systolic
pressure is considered the greatest risk factor for cardiovascular
disease.
That is one reason the new finding is especially
significant, says Dr. Weder.
"This gene variation may be useful in developing
a predictor of which patients are likely to have a rapid rise in blood
pressure as they age, and may need more aggressive monitoring and treatment," he
says.
However, he and his co-authors say, no one gene
variation is enough to predict an individual person's blood pressure
tendencies, and further research on the genes involved in hypertension
will be needed.
The other important implication of the finding is
to create a fuller understanding of dopamine's action in the kidneys,
and changes in that action brought about by variations in the receptor
gene.
Dopamine in the kidney helps the body respond to
large loads of sodium, or salt, coming into the body.
After a salty meal, for example, higher levels of
dopamine can be detected in the urine after being produced and used
by the kidneys to regulate the removal of salt from the body.
Always consult your physician for more information. |
