Study of twins reveals genetic effect on Covid-19 symptoms

Symptoms of Covid-19 appear to be partly down to genetic makeup, researchers at King’s College London have discovered.

The finding is based on data collected through the Covid-19 Symptom Tracker app, launched by the team last month.

While members of the public are encouraged to use the app to track how they feel day to day, the team also asked thousands of twins in the UK, who were already part of another research project, to use the app and record whether they had symptoms or not. The team employed machine-learning algorithms, together with data from the 2.7 million app users – many of whom have been tested for coronavirus – to work out the combination of symptoms that indicate an individual is likely to have Covid-19.

The team then focused on data from just over 2,600 twins to try to establish whether the symptoms experienced by those predicted to have Covid-19 was related to genetic makeup.

“The idea was to basically look at the similarities in symptoms or non-symptoms between the identical twins, who share 100% of their genes, and the non-identical twins, who only share half of their genes,” Prof Tim Spector, one of the scientists leading the endeavour, told the Guardian. “If there is a genetic factor in expressing the symptoms then we’d see a greater similarity in the identical [twins] than the non-identical [twins] and that is basically what we showed.”

The study, which has not yet been peer reviewed, took into account whether the twins were in the same household, with the results revealing that genetic factors explained about 50% of the differences between people’s symptoms of Covid-19.

More specifically, the team found a substantial genetic influence for the symptoms of fever, diarrhoea, delirium, and losses of taste and smell. By contrast, a hoarse voice, a cough, skipped meals, chest pain, and abdominal pain were not linked to genetic makeup.

“I think you can say that your likelihood of getting it at all, or getting it severely, is under some genetic control.”

The team hopes the findings will help scientists ascertain the mechanisms by which Covid-19 acts on the body, as well as offering a possible way to predict those most at risk from the disease.

“Understanding how symptoms of [the disease] Covid-19 pass through the population may indicate the pathogenic mechanisms of [the virus] Sars-CoV-2 infection, as well as offering utility in the allocation of scarce healthcare resources, particularly intensive care beds,” the team writes.

They say the results could also help researchers around the world identify genetic variants that play a role in explaining why some individuals show no, or only mild, symptoms of Covid-19, which could in turn aid the development of drugs for the disease.

But there were other possible targets, Spector said, noting that genetics were closely linked to the immune system and microbes found in the gut.

“It reassures everyone that it is worth exploring this whole triangle of genes, immune system and gut microbes,” he said.