A new study found that the same genetic risk factors that make some people more susceptible to high cholesterol may also increase the risk of Alzheimer's disease.
Without knowing the causes of Alzheimer's disease, scientists at the universities of Washington, St. Louis and California, San Francisco, are conducting the largest study of DNA so far, looking for pre-programmed risk factors.
"We have already known that one of the genes associated with the risk of Alzheimer's disease involves molecules involved in the movement of cholesterol across the body," the scientists said, confirming that the relationship between cholesterol and Alzheimer's may be stronger than previously thought.
Through the new genetic analysis, scientists discovered that a small group of genes, associated with high risk for both Alzheimer's disease and heart disease.
One of the forms of the APOE4 gene, for example, is currently an indicator of the risk of Alzheimer's disease that we know. This type of APOE4 gene has been linked to an increased risk of Alzheimer's disease But they are also present in the healthy, and therefore far from being an indicator of the disease.
"The nature of the risk is variable in the presence of this gene in some healthy people, but we also see a large prevalence of it in people with disease," said one study co-author from the University of Washington, Dr. Celeste Carth, a psychiatrist in St. Louis. This part of DNA affects the brain and its function, but we know how closely it relates to cardiovascular disease. "
When the APOE4 gene works properly and provides a specific protein, this protein is linked to the lipids that make up the lipid proteins, and these molecules help to make sure that the fat goes through the bloodstream properly.
These water-soluble lipid proteins are essential to ensure that the "good" cholesterol of the fatty acids is transferred to tissues that absorb it for energy, and that "bad" cholesterol is redirected to the liver.
If the "bad" cholesterol does not move back to the liver properly, it can accumulate instead in the blood vessels, limiting the flow of blood through it.
This, of course, increases the pressure on the heart, which pumps very hard blood through narrow passages. Therefore, those who have a defect in this gene are more likely to have high cholesterol.
The gene may also have a relationship to the accumulation of amyloid plaques in the brain, which scientists suspect is among the underlying causes of Alzheimer's disease.
The authors of the new study, by researching the DNA of 1.5 million people, found that 90 percent of DNA can be associated with those with risk factors for heart disease, diabetes, high cholesterol and high BMI.
"This study has done two things to strengthen this relationship between fat-related genes and the risk of heart disease and Alzheimer's," says Dr. Karsh.
"Fat is really important for healthy brain cells of all kinds, playing an important role in the ability of cells to transport these pathogenic proteins, as well as the ability of the cell to break down these pathogenic proteins," he said.
The research team also found that some genetic variants related to the immune system have increased the risk of Alzheimer's disease.
In theory, a low-fat diet would mean that there would be a shortage of cholesterol that needs to be removed from the blood stream, which somewhat reduces the importance of genetic ability to transport cholesterol from the blood.
Thus, maintaining low cholesterol may also help reduce the risk of amyloid proteins that accumulate in the brain and thus reduce the risk of developing Alzheimer's. This also suggests that drugs that aim to control cholesterol may be useful to reduce the risk of Alzheimer's disease.