A risk gene that may trigger Alzheimer’s disease

Chris Hemsworth, the actor known as Thor, carries a copy of the APOE4 gene. This diagnosis, along with information that he was at high risk for Alzheimer’s disease, was widely reported some time ago.

A new work by Spanish scientists now underlines this assumption – you can read more about it here. Let’s get to a short, simplified definition first: APOE4 stands for apolipoprotein E. This protein plays an important role in lipid metabolism and exists in three forms: APOE2, APOE3 and APOE4. People who carry two copies of APOE4 have a 15-fold increased risk of developing Alzheimer’s disease. These individuals are also known as APOE4 homozygotes. About two percent of the population is affected, and actor Chris Hemsworth is one of them.

APOE4 has long been known as an Alzheimer’s risk factor. “Over the years, it has become clear that APOE is not only a risk factor, but a causative gene for Alzheimer’s disease,” says Alfredo Ramirez (Cologne University Hospital). The authors of the current study, published in “Nature Medicine,” conclude that APOE4 is the genetic form of Alzheimer’s disease.

That’s because their study showed that nearly all APOE4 homozygotes have Alzheimer’s disease. “APOE4 homozygotes showed significantly more biomarkers of Alzheimer’s from age 55 than APOE3 homozygotes,” explains Elisabeth Stockmann, head of the Outpatient Clinic for Memory Impairments and Dementia at the Medical University of Vienna. Also: “At age 65, nearly all APOE4 homozygotes had abnormal amyloid levels in CSF, and 75 percent had positive amyloid scans, with concentrations increasing with age.” In Alzheimer’s patients, amyloid clumps together in the brain to form deposits – called plaques. In addition, the study also showed that the first symptoms of Alzheimer’s disease appeared seven to ten years earlier in APOE4 carriers than in APOE3 homozygotes.

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Accusative knowledge

Although meaningful, the findings of this study are unlikely to lead to severe changes in Alzheimer’s patients or carriers of the APOE4 gene. On the one hand, the onset of Alzheimer’s disease cannot (yet) be predicted with certainty, and on the other, “knowledge of a genetic risk factor can be stressful,” explains Stockman. For this reason, she generally does not consider testing for APOE4 before symptoms appear necessary. His colleague, Alfredo Ramírez, of the University Hospital of Cologne, said it was difficult to determine the right time for such a test. “Genetics says something about probability, but not about fate.”

Nicolai Franzmeier from the Ludwig Maximilian University of Munich (LMU) also mentions treatment options: “I currently do not recommend testing for APOE4 due to the lack of any therapeutic effects. So you have to live with the outcome first, above all, with knowledge, but sometimes you feel helpless because medicine can’t really do much at this point.” Lifestyle changes are known to help postpone symptoms.

This means: getting enough exercise, eating healthily and keeping other vascular risk factors such as high blood pressure under control. However, it is questionable whether a genetic disease can be completely stopped, the expert says. “In the future, APOE4 genotyping will certainly become relevant for early diagnosis and treatment, if we manage to develop sensible treatment approaches.”

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