Alzheimer's can affect us all – but women develop the disease significantly more often than men. Overall, two-thirds of those affected are women, which corresponds to about 800,000 people in Germany. For a long time, researchers attributed this imbalance to the longer life expectancy of women, as the greatest risk factor for Alzheimer's disease is age.
However, we now know that the probability of a woman developing Alzheimer's is higher than that of a man, regardless of their respective life expectancy.
In recent years, the female hormonal balance has increasingly come into focus as a cause. A new review article from the journal Neuroforum now shows that causes can also be found in sex-specific genes. The authors, PD Dr. Alex Yang Liu and Prof. Klaus Faßbender from Saarland University Hospital, have identified three factors that are presumed to contribute to women developing Alzheimer's more frequently. On the occasion of International Women's Day on March 8, the non-profit Alzheimer's Research Initiative (Alzheimer Forschung Initiative e.V.) provides information on the new findings.
Factor 1: Impaired blood flow in the brain
Impaired blood flow in the brain occurs in around 80 percent of Alzheimer's patients. One cause is the degradation of pericytes. These are cells that regulate blood flow in the brain. When the number of pericytes decreases, the brain is no longer adequately supplied with oxygen and cognitive abilities decline. In addition, harmful deposits of the protein beta-amyloid can increasingly accumulate in the brain, which are presumed to lead to the death of nerve cells. The genes that control the function of pericytes are located on the male and female sex chromosomes. This leads to different regulation of pericytes.
Factor 2: Disruption of information transmission in the brain
Gender also influences information transmission in the brain in Alzheimer's disease. Certain cells, called oligodendrocytes, ensure that nerve cells are protected and that information can be exchanged quickly. There are indications that in the case of Alzheimer's disease, these oligodendrocytes are activated less strongly in women than in men. As a result, this protective layer is less well maintained in women, and information transmission in the brain is more severely impaired. These processes are presumably controlled by genes in the reproductive organs, in the testes in men and in the ovaries in women.
Factor 3: Weakened Immune Defense
Microglia cells are an important part of the brain's immune defense. In a healthy brain, they have an anti-inflammatory effect and act like a kind of garbage disposal, removing harmful substances. In Alzheimer's disease, microglia cells are initially still able to break down harmful protein deposits typical of the disease in the brain. As the disease progresses, the microglia cells become increasingly exhausted due to constant activation. They can no longer guarantee the protection of the brain, but instead cause chronic inflammation, which further promotes the degradation of nerve cells.
Microglia cells are influenced by various factors, which are also dependent on sex. In women, the immune defense and the regulation of inflammatory processes appear to function less well than in men. "Sex also influences immune and inflammatory responses because many genes related to immune responses are located on the X chromosome," says Yang Liu. Women have two X chromosomes, while men have one X and one Y chromosome.
