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Infectious Diseases

Updated 19 May 2020

Why are certain people more at risk if infected with Covid-19? Scientists may have a clue

Statistics show that the elderly and those with co-morbidities appear to be in a high-risk category, if infected with Covid-19. But why is this?

From the beginning of the Covid-19 outbreak, health authorities have listed people older than 60 and those with chronic disease in the high-risk category for coronavirus.

Now, investigators reported that a group of tiny RNA that would usually attack SARS-CoV-2, the virus that causes Covid-19, as soon as it tries to infect the body, diminish with age and chronic health problems.

What exactly are these tiny RNAs?

MicroRNAs are a class of non-coding DNA that play a role in gene expression in our bodies. Gene expression is a tightly regulated function in the body where a cell is allowed to respond to its changing environment.

A simple example of this in the human body is when microRNAs control insulin expression and release a signal that blood glucose needs to be regulated.

When we refer to “measuring” your gene expression, it’s the ability to see at what level a particular gene will be expressed, for example, how likely you are to develop a certain type of cancer.

Covid-19 and your microRNAs

With ageing, and in the case of chronic disease, the levels of microRNAs that are responsible for so many regulations in your body are starting to dwindle, which also affects your ability to fight off various infections from bacteria and viruses, according to Dr Carlos M. Isales, co-director of the MCG Center for Healthy Aging and chief of the MCG Division of Endocrinology, Diabetes and Metabolism.

It’s basically the same as not having enough troops on the ground of a war – with diminished microRNAs, the SARS-CoV-2 can attack and do what it naturally does, i.e. take over cells, replicate and ultimately make you ill, according to the research in the journal Aging and Disease.

This study focused on the RNA sequence of two coronaviruses – SARS-CoV, which caused the 2003-outbreak and SARS-CoV-2, the current coronavirus and the sequence of microRNAs that are likely to attack the virus.

"The most important and striking feature of Covid-19 is the increased case fatality rate in aged individuals, especially those over the age of 65," the researchers wrote in the study. 

And what about younger people who also succumb to Covid-19? Isales investigated and explained that our body’s microRNAs would usually target the virus unless they are outnumbered.

Could this be the solution?

"Normally your immune cells would go in and destroy them, but you have this large viral load as they continue to replicate and you have all this abrupt inflammatory response," says Isales. This can ultimately cause a person with Covid-19 to become very ill, and the outcome can be fatal.

"My perspective is there is a key set of microRNAs that are important in triggering this abnormal response in making older patients more susceptible," said senior author Isales. "We are looking at microRNAs in general dropping, but there is a specific subset that is key. The question is whether we can target those as a therapy."

Could this be the solution, leading to a treatment?

 Dr Sadanand Fulzele, co-author and ageing researcher in the Department of Medicine and Center for Healthy Aging at the Medical College of Georgia at Augusta University, stated that they are moving towards producing synthetic microRNA that could potentially help those weakened by age or disease.

Future studies will be needed to determine which microRNA will be best suited as a therapy. Right now, guidelines worldwide recommend that people aged 60 and older and people of any age with underlying conditions should take extra precautions not to become infected with SARS-CoV-2.

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