The clinical features of patients affected by COVID-19 are under much scrutiny. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19 disease, has infected over 50 million people worldwide and claimed over 1.25 million lives. In the UK alone, nearly 50,000 people have succumbed to this virus. Therefore, it is vital to investigate the conditions that increase the risk of COVID-19 infection and cause death. The predisposing factors contributing to increased transmission and clinical severity remains unclear.
It is well known that people with medical conditions such as diabetes, cardiovascular and respiratory pathologies, and hypertension, and especially the elderly are highly vulnerable to the virus. Age is a significant risk factor for COVID-19 mortality. The prevalence of neurodegenerative diseases among older people is high; thus, it is important to study Alzheimer's disease and Parkinson's disease in the context of COVID-19.
In a recent medRxiv* preprint paper, Dr. L. Miguel Martins and colleagues from the University of Cambridge investigate the links between neurodegeneration and COVID-19. They explored whether individuals with dementia, Alzheimer's disease, or Parkinson's disease are at increased risk of COVID-19 infection and mortality.
The team made use of the UK Biobank, analyzing primary health records of 13,338 UK individuals tested for COVID-19 between March and July 2020. The UK Biobank contains health data from over 500,000 community volunteers living in England, Scotland, and Wales. 1,626 out of the 13,338 individuals tested positive for COVID-19 between March 16 and July 26, 2020.
Consistent with previous observations, the team found that a diagnosis of dementia was associated with the highest risk of mortality from COVID-19, followed by male gender, increasing age, and social deprivation.
Next, the researchers analyzed the different types of dementia and their association with COVID-19. Among COVID-19 positive patients in the cohort, The overall cumulative incidence of Parkinson's disease and Alzheimer's disease diagnosis was 1.7% and 1.6%, respectively.
Diagnosis of Alzheimer's disease was strongly associated with COVID-19 infectivity; Parkinson's disease diagnosis was not as strongly associated with COVID-19 infectivity.
It is important to note that in this study model, pre-existing diagnosis of cancer was negatively associated with COVID-19 death. Also, there was no significant association between diabetes, C-reactive protein levels, and ethnicity.
However, the diagnosis of frontotemporal dementia and Alzheimer's disease were associated with the greatest risk of COVID-19 death, unlike Parkinson's disease or vascular dementia. Independently from age, sex, and other comorbidities, the study informs that participants with Alzheimer's are at higher risk of dying from COVID-19. The COVID-19 mortality among patients with Parkinson's disease and vascular dementia does not differ from the general population.
This study shows: 1) pre-existing diagnosis of Alzheimer′s disease predicts the highest risk of COVID-19 infection and mortality, and 2) in the case of Parkinson′s disease patients, the risk of infection is increased but not mortality from COVID-19.
In one of the most extensive cohort studies of COVID-19 in Europe, dementia was found to be the most common comorbidities in COVID-19 patients. Another study showed that people with dementia and other neurological diseases are at higher risk of hospitalization and death due to COVID-19. Also, 25.6% of all COVID-19 deaths between March and June 2020 are found in people with dementia - the most common pre-existing conditions associated with COVID-19 mortality.
While the previous studies provide compelling evidence that dementia or neurodegenerative diseases increase the risk of COVID-19 infection and mortality, but it does not specific subtypes of neurological disorders that may differentially affect COVID-19 outcome. The important conclusion drawn from this study is that there are disease-specific differences in COVID-19 susceptibility, especially among patients affected by neurodegenerative disorders.
This study is a robust analysis, using granular data from the UK Biobank- where all participants in their dataset have received COVID-19 testing. Mostly other similar studies were limited to hospitalized individuals - not reflecting the community settings. Because many are asymptomatic, this screening protocol used here is more sensitive for analyzing COVID-19 infection and mortality rates among people diagnosed with neurological diseases.
While previous studies suggest that dementia increases susceptibility to COVID-19, this study provides the first systematic analysis of the relationship between COVID-19 and neurodegenerative diseases at the individual level.
These results highlight the importance of disease-specific neuropathology and management in the potential susceptibility to COVID-19.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.