March 5, 2012
Five mutations linked to platelet counts in African-Americans
Researchers’ findings could lead to better drugs for coronary artery diseases
Researchers led by scientists from Johns Hopkins have found five previously unknown gene mutations believed to be associated with elevated blood platelet counts in African-Americans, findings they say could someday lead to the development of new drugs to help prevent coronary artery disease.
The study is believed to be the first of its size to focus on platelet genetics in African-Americans, who have a higher risk of stroke than other racial groups. They also have relatively higher platelet counts and average platelet volume, and worse outcomes than whites after a heart attack.
“Improving our understanding of the biology and genetics of platelets and how they function will aid us in developing better and more individualized treatments to reduce risk of heart disease associated with platelets,” said study leader Rehan Qayyum, an assistant professor in the Division of General Internal Medicine at the Johns Hopkins University School of Medicine.
Qayyum cautions that there are believed to be many more genes involved in platelet function that remain unknown.
Platelets are cells, smaller than red or white blood cells, that are produced in bone marrow and foster blood clotting. While clotting is critical to stop bleeding after injuries, it also can cause harm by allowing clumps of blood cells to clog blood vessels leading to the heart, brain and other organs, cutting off blood flow.
Studies have shown that the greater the platelet volume or count in the blood, and the larger the platelets, the greater the risk of dangerous clot formation. Qayyum notes that the number of platelets in a given amount of blood (platelet count) and the size of these platelets (measured as average platelet count) vary from person to person in much the way that height, weight and eye color traits differ. Thus, he said, the search for genes that control this variation is a potentially fruitful line of scientific inquiry.
Qayyum and his colleagues, publishing in the online journal PLoS Genetics, report that they conducted a meta-analysis and genomewide association study, looking at genetic data from 16,000 African-American participants in seven studies. Comparing information from each study, they tracked 2.5 million single possible changes in the human genetic code to see which genes stood out across the entire group as significantly associated with increased or decreased platelet counts.
Across the studied genomes, the researchers found five such alterations—involving the addition or deletion of a single piece of genetic code—that had not been identified in other populations. When they checked their findings against data from Caucasian and Hispanic groups, they found three of the novel gene mutations in those populations, too. Four of the previously unknown gene mutations were later found in the genetic code of platelet cells, but one was not; that one, however, was found close to a gene that is known to be essential in the formation of normal platelets. The exact role played by each of these mutations still needs to be determined, Qayyum says.
Qayyum says that one goal of the research is to identify new targets for drugs that decrease platelet aggregation in the arteries and prevent clot formation. Blood thinners—including aspirin, clopidogrel and warfarin—are widely used anti-platelet medications, but some people can’t tolerate the side effects, which include bleeding, bruising and gastrointestinal upset.
The study was supported by the National Heart, Lung and Blood Institute.
In addition to Qayyum, Johns Hopkins researchers involved in the study are Lisa Yanek, Diane M. Becker and Lewis C. Becker.