In a new study, researchers at Washington University School of Medicine in St. Louis have discovered five common genetic variations, which elevate the risk of metabolic syndrome, a group of factors linked to heart disease and diabetes.
The research team has also identified one more variant, which appeared to protect against the condition.
Those suffering from metabolic syndrome have at least three of the following symptoms: abdominal obesity, high blood triglyceride levels, lower good cholesterol (HDL), elevated blood pressure and elevated fasting blood glucose. In fact they are more susceptible to develop heart disease and diabetes than those without metabolic syndrome.
The study was aimed to determine changes in the CD36 gene, which is located in a region of chromosome 7 that has been linked to metabolic syndrome in several genome-wide studies.
According to the researchers, better understanding of the relationships between obesity, the CD36 gene and disease risk may facilitate earlier identification of individuals who are more susceptible to develop metabolic syndrome. This may lead to early treatments such as medication or lifestyle changes, perhaps preventing or delaying future problems with diabetes or heart disease.
Senior investigator Nada A. Abumrad, Ph.D., the Dr. Robert C. Atkins Professor of Medicine and Obesity Research, first identified the CD36 protein in studies with mice, in which they showed that the protein facilitates the use of fatty acids for energy. CD36 is located on the surface of cells and distributed throughout many tissues, including fat cells, the digestive tract, heart and skeletal muscle.
In the study, the researchers focused on 36 small genetic variations, called single nucleotide polymorphisms (SNPs), in the CD36 gene. A SNP involves a single base-pair change in the DNA. They examined DNA taken from more than 2,000 African-Americans and hope that these findings also will be applicable in other populations.
"The idea was to look at the different variations in the gene and see whether they were more prevalent in people who also had elevated cholesterol, abnormal blood glucose or the other components of the metabolic syndrome," said first author Latisha Love-Gregory, Ph.D., research instructor in the Division of Geriatrics and Nutritional Science.
According to Love-Gregory, they have demonstrated a link between SNPs in the gene and metabolic syndrome.
"There is additional work to do to determine if the function of these genetic variants actually contributes to the development of type 2 diabetes or heart disease. We do expect that a number of different changes, in both CD36 and other genes, will be related to these diseases. What we'd like to learn, however, is whether the changes identified in the gene alter the CD36 protein in ways that change its function to make a person more vulnerable," she explained.
They found that five of the SNPs they examined are more common in people who have metabolic syndrome symptoms, but a sixth seemed to have a more favorable metabolic effect. The "protective" SNP makes people produce lower amounts of CD36 protein.
In this study, people who had the protective variant on only one of their copies of chromosome 7 were less susceptible to metabolic syndrome. But people with two copies of the variant, who were completely deficient in the CD36 protein, did not appear to be protected. They tended to have lower levels of HDL, the so-called good cholesterol.
"A bit less CD36 protein may improve your risk profile, but people need some CD36 function. It's like requiring a certain level of fat in the diet. Fatty acids are important for optimal function of many tissues - from pancreatic beta cells to skeletal muscle to the heart - but too much fat creates a problem," said Abumrad.
They found that many variants influenced blood levels of HDL cholesterol. Now they are taking a closer look at the relationship between CD36 and HDL cholesterol. Higher levels of HDL normally are considered positive, but because changes in the CD36 gene seem to influence HDL, the researchers want to make sure that the HDL molecule isn't being altered in composition or function.
The study is published in the June issue of the journal Human Molecular Genetics.