March 31, 2011 -- Mothers with a certain genetic mutation may pass the tendency to develop high blood pressure on to their children, according to a new study.
Researchers from the U.S., China, and Austria made the discovery after focusing on a five-generation Chinese family. Many of its members who descended from the same female ancestor had high blood pressure.
The researchers found in these people a genetic mutation that affects the mitochondria. These are the ''powerhouses'' of the cells that convert energy into useable forms. The discovery suggests that a mitochondrial DNA mutation could be the basis for high blood pressure in some people.
"This mutation can reduce the cellular energy production," says researcher Min-Xin Guan, PhD, a professor of genetics at Zhejiang University in China. That increases the production of free radicals, substances which can be damaging to cells, his team found.
''These mitochondrial dysfunctions may contribute to the development of hypertension," Guan writes.
More than 60 million people in the U.S. have high blood pressure, according to the American Heart Association. More than two-thirds require medication for the condition. Untreated high blood pressure increases the risk for both stroke and heart attack.
The new study is published in Circulation Research, a journal of the American Heart Association.
Maternal Transmission of High Blood Pressure
Guan and his team evaluated 106 people from a large Chinese family. The investigation began after one of its members developed high blood pressure at age 45.
The researchers examined her but could find no abnormalities to explain the elevated pressure. They went on to interview other family members. They found 15 of the 27 maternal relatives had high blood pressure even after treatment. Only seven of the 81 non-maternal relatives did.
None of the offspring of the affected fathers had high blood pressure.
Because the high blood pressure was maternally transmitted, the researchers suspected involvement of the mitochondrial DNA. When children are born, they get half their chromosomal DNA from one parent, half from the other. However, mitochondrial DNA is passed entirely from a mother to a child.
So the researchers analyzed the mitochondrial genome of the maternal relatives. They found a mutation on the mitochondrial tRNA-Ile gene, involved in reducing cellular energy production.
While the finding appears to have no immediate use to patients, it may eventually aid treatment approaches, says Thomas Giles, MD, professor of medicine at Tulane University School of Medicine, New Orleans, and past president of the American Society of Hypertension. He reviewed the study findings for WebMD.
An increase in free radicals seen with this mutation leads to a decrease in nitric oxide, which helps keep blood vessels relaxed, Giles says. As they constrict and narrow, high blood pressure can result.
If the research bears out, Giles say, this type of high blood pressure linked to mitochondrial malfunction will probably explain a very small percent of total cases.
Eventually, scientists may find out how to repair this genetic defect, he says.
One weakness of the study is that the exact mechanism of how the mutation leads to the high blood pressure is not known for sure, says Donna Arnett, MD, professor and chair of epidemiology at the University of Alabama at Birmingham School of Public Health. She is a spokeswoman for the American Heart Association.
However, the research might lead to a genetic screening test in the future, she says.
Blood pressure is considered high when the systolic pressure is 140 or more and the diastolic is 90 or more. Systolic is the upper number of the blood pressure reading. It reflects pressure when the heart contracts. Diastolic, the lower number, reflects the pressure when the heart relaxes.