A certain gene mutation known as APOE4 has long been known to raise the risk for Alzheimer's disease.
Now, researchers report it may also predispose people to increased susceptibility to COVID-19 infection and severe symptoms, including small brain bleeds.
Researchers in Finland, where about one-third of people carry the APOE4 mutation, studied the link between the mutation and severe COVID-19. They also studied microscopic brain changes in the cadavers of people who died from COVID-19 and looked at symptoms of long-term mental fatigue experienced by some survivors.
"The common e4 allele of the APOE gene appears to be associated with a heightened risk of severe COVID-19 in the Finnish population. The significance of APOE4 is emphasized in the Finnish population, which may be due to its genetic homogeneity," said researcher Dr. Liisa Myllykangas, a consultant neuropathologist from the University of Helsinki.
The team found that the risk of developing COVID-19 that requires intensive care more than doubled in those with the APOE4 mutation. More microscopic brain bleeds that occurred as a result of severe COVID were also found in carriers of this mutation.
Co-author Dr. Johanna Hästbacka, from Helsinki University Hospital, said APOE4 may also affect the severity of certain "long COVID" symptoms, including difficulty with attention and concentration.
The team used data from the FinnGen project, which combines genome data produced from biobank samples with health data compiled from national registries. This study was based on the data of 46,000 people, more than 2,600 of whom were diagnosed with COVID.
Myllykangas noted that the number of COVID patients in the study was small and more research is needed.
An important question not answered in the study is the connection between COVID-19 and the onset of memory disorders in APOE4 carriers, the researchers said.
"To answer this question, long-term follow-up studies on patients recovered from COVID-19 are needed, as is basic research focused on the combined effects of APOE4 and systemic inflammation on the mechanisms of memory in the brain. Our research group has already launched these lines of further research at the University of Helsinki and HUS [Helsinki University Hospital],” Myllykangas said in a university news release.
The team published its findings recently in the journal Acta Neuropathologica Communications.