Figure 1: Recent studies reveal that COVID-19 may be associated with neurological diseases, in particular Alzheimer's Disease.
Source Credit: Harvard Health Publishing (LINK)
COVID-19 is one of the most feared diseases today, especially for the elderly. Due to their weak immunity and underlying health conditions, seniors struggle to recover from the virus. To make matters worse, recent research discovered that coronavirus may hasten the progression and symptoms of Alzheimer’s Disease (AD). George Vavougios, a postdoctoral researcher at the University of Thessaly, conducted a study examining cognitive impairment in COVID-19 patients—their average age being 61—two months after being discharged from the hospital. Vavougios discovered that the patients did experience cognitive decline even after being discharged.
According to a recent study led by Cleveland Clinic, there has been an increase of COVID-19 patients with persisting neurological complications even after recovering from the infection. This finding suggests a possibility of coronavirus having long-term impacts on brain function. Scientists first searched for the virus in the patients’ brains, which they were not able to find any trace of. Consequently, researchers turned to a different method to test the possible correlation between coronavirus and AD. Using artificial intelligence and COVID-19 patients with AD, they measured the proximity between the SARS-CoV-2 gene and the genes of several neurological diseases–closer proximity indicated that the virus and neurological disease share pathways. In addition, scientists also analyzed the genetic factors that allow the coronavirus to infect brain tissues. Although they found little evidence that the virus targets the brain directly, researchers discovered a close network between the SARS-CoV-2 gene and the genes of several neurological diseases. In particular, there was a marked association between the genes of COVID-19 and AD.
To extend the finding, researchers also investigated how COVID-19 may be related to typical symptoms of AD–neuroinflammation, and brain microvascular injury. The investigation revealed that SAR-CoV-2 infection alters the markers of AD and increases the expression of certain viral entry factors in the cells of the blood-brain barrier. The blood-brain barrier is blood vessels surrounding the brain that regulates the movement of ions, molecules, and cells between the blood and the brain. More expression of the viral entry factors in the blood-brain barrier means that viruses could enter the brain more easily.
"These findings indicate that the virus may impact several genes or pathways involved in neuroinflammation and brain microvascular injury, which could lead to Alzheimer's disease-like cognitive impairment,” says Dr. Feixiong Cheng, assistant staff in Cleveland Clinic's Genomic Medicine Institute.
An experiment conducted by Gabriel de Erausquin, professor of neurology at UT Health San Antonio, discovered significant findings as well. For his study, more than 400 Argentine adults–ages 60 or older–who tested positive for coronavirus were included. De Erausquin and his team measured the patients’ cognitive abilities, emotional reactivity, motor function, and coordination for a span of three to six months. During this research, he found that first, people who were infected with the coronavirus had problems with memory. Second, the severity of the COVID-19 patients’ illnesses did not predict their cognitive problems. And third, that the loss of ability to smell may be related to cognitive impairment.
Despite multiple studies suggesting a strong correlation between COVID-19 and neurological diseases, De Erausquin says it is too early to make any conclusions. Moreover, he mentions that even if there is an association between the two, there still remains the question of whether these issues may be permanent or temporary.
“If you have covid, it doesn’t necessarily mean you’re at an increased risk for dementia or Alzheimer’s,” says Heather M. Snyder, vice president of medical and scientific relations of Alzheimer’s Association. She believes that further research is still necessary on this subject. “We're still trying to understand what that relationship is.”
Q&A:
Sally: Can you explain more about the SARS-CoV-2 gene? What are some other diseases that COVID-19 might have a correlation with?
SARS-CoV-2 is the official name of coronavirus. Scientists conducted an analysis on the gene and discovered that it had the highest correlation with SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). Unfortunately, the drugs that were used to combat SARS-CoV and MERS-CoV were ineffective against SARS-CoV-2.
Jennah: Your article focuses mostly on the investigation of Alzheimer’s Disease and COVID-19. Are there any other neurological diseases that scientists have conducted (or are conducting) research on? Are these cognitive associations only seen in elders, or are there other age groups that could show similar responses as well?
Scientists are currently conducting research on other neurological diseases. They expect that other neurological complications like stroke, neuromuscular disorders, and meningoencephalitis will be reported. And so far, the research shows a higher association in elders because neurological diseases are more common in seniors. However, that doesn’t mean cognitive associations can’t be seen in younger patients as well.
Xavier: You mention that the SARS-CoV-2 gene increases the expression of entry factors in the cells of the blood-brain barrier, which in turn makes it easier for viruses to enter the brain. Does this make the human body more vulnerable to other diseases as well?
This is a topic that is still being researched by many scientists. It seems possible that other viruses could pass through the blood-brain barrier. However, scientists are trying to find out if this is only possible with SARS-CoV-2.
John: How were the measurements made in De Erausquin’s study, and were they statistically significant? If so, to what extent?
The way that De Erausquin measured their cognitive abilities was through several questions. He assessed them based on questions like “Could the patients recall names and phone numbers?” “Can they remember where they put things?” or “Could they retrieve the right word at the right time?” They are statistically significant because his study encompassed a large number of patients.
Wooseok: Does the virus directly damage the brain (by attacking the brain cells), or is the loss of memory caused by an indirect factor of the virus?
So far, scientists have found no evidence of the virus directly harming the brain. In fact, many of the neurological symptoms of COVID-19 are due to the body’s widespread immune response. So the virus indirectly causes memory losses and other cognitive impairments.
Anna: You mentioned that loss of the ability to smell may be correlated with cognitive impairment. How?
Cognitive impairment is related to the sense of smell because it is handled directly by our brain’s olfactory bulb. The olfactory bulb is a structure in front of our brain that sends information to other parts of our body. Thus, if our brain is damaged or affected, it can lead to the loss of the ability to smell.
Fabian: What are some neurological symptoms of coronavirus for patients under the age of 60? Are neurological side effects not as important to the younger patients as the old patients?
Patients under the age of 60 can experience similar neurological symptoms as those who are older than 60—especially if they were also suffering from a neurological disease. Neurological side effects are important to all patients; however, because it is not as common in younger patients, most of the study revolves around older patients.
Works Cited
Anderson, Pauline. “COVID-19 Tied to Acceleration of Alzheimer's Pathology.” Medscape, Medscape, 30 July 2021, www.medscape.com/viewarticle/955755.
Haupt, Angela. “Covid-19 Could Lead to Cognitive Decline, Especially among Older Adults, New Research Suggests.” The Washington Post, WP Company, 29 July 2021, www.washingtonpost.com/lifestyle/wellness/dementia-alzheimers-covid-research-link/2021/07/29/bccef096-f07d-11eb-a452-4da5fe48582d_story.html.
“Study Identifies How COVID-19 Linked to Alzheimer's Disease-like Cognitive Impairment.” ScienceDaily, ScienceDaily, 10 June 2021, www.sciencedaily.com/releases/2021/06/210610162405.htm.
Naqvi, Ahmad Abu Turab, et al. “Insights into Sars-Cov-2 Genome, Structure, Evolution, Pathogenesis and Therapies: Structural Genomics Approach.” Biochimica Et Biophysica Acta. Molecular Basis of Disease, Elsevier B.V., 1 Oct. 2020, www.ncbi.nlm.nih.gov/pmc/articles/PMC7293463/.
Ghannam, Malik, et al. “Neurological Involvement of CORONAVIRUS DISEASE 2019: A Systematic Review.” Journal of Neurology, Springer Berlin Heidelberg, Nov. 2020, www.ncbi.nlm.nih.gov/pmc/articles/PMC7304377/.
“Coronavirus and the Nervous System.” National Institute of Neurological Disorders and Stroke, U.S. Department of Health and Human Services, Sept. 2021, www.ninds.nih.gov/Current-Research/Coronavirus-and-NINDS/nervous-system.
Walsh, Colleen. “How Scent, Emotion, and Memory Are Intertwined - and Exploited.” Harvard Gazette, Harvard Gazette, 27 Feb. 2020, news.harvard.edu/gazette/story/2020/02/how-scent-emotion-and-memory-are-intertwined-and-exploited/#:~:text=Smells%20are%20handled%20by%20the,related%20to%20emotion%20and%20memory.
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