Results of a pioneering study may provide new clues to treating and preventing hypertension in African-Americans. Hypertension, or chronic high blood pressure, underlies an array of life-threatening conditions, including heart disease, stroke and kidney disease. About one-third of U.S. adults suffer from the condition, but its occurrence is greater among African-Americans, with 39 percent of African-American men and 43 percent of women affected.
Earlier this year, researchers from the National Institutes of Health, the country’s medical research agency, in collaboration with scientists from the Coriell Institute for Medical Research in Camden, N.J., Boston University and Howard University, discovered five genetic variants related to blood pressure in African-Americans. It was the first time that the relatively new genome-wide association study had focused on blood pressure and hypertension in an African-American population.
“We hope these findings eventually will translate into better ways of helping the millions of African-Americans at risk for hypertension, as well as improved treatment options for other populations,” says Eric Green, M.D., Ph.D., scientific director at the NIH’s National Human Genome Research Institute (NHGRI).
The researchers analyzed DNA samples from 1,017 participants in the Howard University Family Study, a multigenerational study of families from the Washington, D.C., metropolitan area who identified themselves as African-American. Half of the volunteers had hypertension and half did not. Blood pressure is measured in millimeters of mercury (mmHg) and expressed with two numbers; for example, 120/80 mmHg. The first number (systolic pressure) is the pressure when the heart beats while pumping blood. The second number (diastolic pressure) is the pressure in large arteries when the heart is at rest between beats.
The researchers scanned the volunteers’ DNA, or genomes, and found five genetic variants significantly more often in people with hypertension than in those without the condition. The variants were associated with high systolic blood pressure, but not with diastolic blood pressure or combined systolic/diastolic blood pressure. “Although the effect of each individual genetic variant was modest, our findings extend the scope of what is known generally about the genetics of human hypertension,” says the study’s senior author, Charles Rotimi, Ph.D., senior investigator for NHGRI and director of the trans-NIH Center for Research on Genomics and Global Health.
In May, two major international studies used the genomewide association approach to identify 13 genetic variants associated with blood pressure and hypertension in people with primarily European and South Asian ancestry. While each variant was associated with only a slight increase in blood pressure, that work found that the more variants an individual had, the greater his or her risk of hypertension. Two genes identified by one of those studies were also associated with blood pressure in the new study.
In their study of African-Americans, the researchers found that all of the five genetic variants associated with blood pressure were located in or near genes that code for proteins thought to be biologically important in hypertension and blood pressure. Previous research had implicated two of those genes in blood pressure regulation. Additional analyses by the Rotimi group revealed that all of the variants are likely involved in biological pathways and networks related to blood pressure and
The Rotimi group also scanned DNA from 980 West Africans with and without hypertension and confirmed that some of the genetic variants detected in African-Americans were also associated with blood pressure in West Africans. “The Western African population is of particular significance since it is the ancestral population of many African-Americans,” says lead author Adebowale Adeyemo, M.D., a staff scientist at the Center for Research on Genomics and Global Health.
An existing class of anti-hypertension drugs, called calcium channel blockers, already targets one of the genes. However, the additional genes may point to new avenues for treatment