BALTIMORE, Jan. 29 (UPI) -- An altered gene protects about a quarter of all African-Americans from coronary artery disease, U.S. researchers say.

A team of scientists, led by Diane Becker and Dr. Brian Kral of Johns Hopkins University in Baltimore, learned a single alteration in the genetic code -- the guanine variant on the gene linked to higher risk of coronary disease in all races -- reduces the likelihood of clogged arteries five-fold in some blacks.

The study, published online in the Journal of Human Genetics, indicates among African-Americans, who have a disproportionately greater genetic risk of coronary heart disease, a subset could inherit a gene variant from each parent and have double the protection against coronary heart disease.

Becker emphasizes most African-Americans lack this protective genetic modification. Only an estimated one-quarter have the protective CDKN2B code, while only 6 percent have two copies, the study says.

"A lot of African-Americans have this protective genetic modification, most do not," Becker says in a statement.

Becker, Kral and colleagues base their results on blood analysis of 548 African-American men and women in the Baltimore region that was confirmed in several hundred more African-Americans in the Atlanta and Durham, N.C., areas. Becker say the analysis was successful because of the large, broad base of volunteer study participants.