Study of twins reveals how genetic make-up can make some people more vulnerable to coronavirus and more likely to experience fever, fatigue and loss of taste and smell

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Genetics make some people more susceptible to coronavirus infection than others, data gathered from a symptom-tracking app suggests. 

The findings are based on information submitted to the 'Covid Symptom Tracker' app, which was launched by researchers at King’s College London last month.

As well as encouraging members of the public to track their symptoms, the researchers asked thousands of twins in the UK, who were already part of another research project, to use the app. 

They then used this data to try and establish whether the symptoms experienced by those predicted to have COVID-19 were related to their genetic makeup.

The results reveal that genetic factors explain about 50 per cent of the differences between people’s symptoms of COVID-19.

These symptoms include delirium, fever, fatigue, shortness of breath, diarrhoea and loss of taste and smell in individuals, they found. 

Other symptoms such as hoarse voice, cough, chest pain and abdominal pain were thought to be a result of the surrounding environment and not genetic make-up.  

The Kings College London project used information regarding twins’ health, symptoms and level of contact with their co-twin to develop a model to understand how much genes influence symptom presentation in COVID-19

The research into identical and non-identical twins, as part of TwinsUK, allows researchers to understand to what extent health and disease is affected by genes – 'nature' – and the environment – 'nurture'. 

'The idea was to basically look at the similarities in symptoms or non-symptoms between the identical twins, who share 100 per cent of their genes, and the non-identical twins, who only share half of their genes,' Professor Tim Spector, a genetic epidemiology at King's College, London and one of the lead developers of the app, told the Guardian. 

'If there is a genetic factor in expressing the symptoms then we’d see a greater similarity in the identical than the non-identical and that is basically what we showed.'

Prevalence of symptoms in TwinsUK study. The highest reported symptoms from the 2,633 adult same sex twins was coughing (in 252 twins), chest pain (216), diarrhoea (167) and skipped meals (157). Right column shows the twins separated by sex

He added: 'This disease is very weird, the way it has a very different presentation in the population in different people – what we are showing is that isn’t random.

'It is not mainly due to where you live or who you have seen – a lot of it is something innate about you.

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

It is hoped the findings – published in a pre-print non-peer-reviewed paper online – could provide scientists with an indication on how to go about developing treatments, as well as helping to identify high-risk groups.  

The 'Covid Symptom Tracker', which collected symptoms data from the twins, is a free app for Android and iOS that lets Brits self-report their health status daily, even if they are feeling well.

The free app for Android and iOS that lets Brits self-report their health status daily, even if they are feeling well

A collaboration between researchers at King’s College London, Guy’s and St Thomas’ hospitals and health data science company ZOE, the tracker provides real-time locations of COVID-19 symptoms as they crop up. 

Collected symptom data aims to help slow the outbreak of COVID-19 in the UK by identifying how fast the virus is spreading in an area, as well as high risk areas of the country.  

Around 48 hours after its launch in late March it became the third most popular free app in Apple's UK store.

It was being downloaded generally at a rate of about 50,000 times an hour, the developers confirmed to MailOnline.       

Some two million people in the UK have downloaded the app, which is helping to inform scientists about the virus's progression.

Users log responses to a variety of health questions daily. The developers aim to launch a web-based version of the app for people without smartphones

However, the number actually using the app fell by almost 75 per cent earlier this month.

In an email to all sign-ups of the app earlier this month, Professor Spector urged people to keep using the app to help the NHS.

'Please keep using the app every day to tell us how you feel, even if you are healthy and have no symptoms,' he said.

'This data is incredibly valuable to help the NHS track the disease in real time and allocate resources where they are needed most. 

'If you could take 30 seconds each day to report how you feel, your individual contribution will play a huge role in our collective effort to beat the disease in the UK.'

Analysis of the data published on April 8 suggests coronavirus lockdown is working, with the number of people aged 20-69 reporting symptoms falling from 1.9 million to 1.4 million across the UK.  

Upon sign-up, users of the COVID-19 tracker have to enter their year of birth, sex, weight, height, postcode and email address.

They then answer general questions about their health, such as whether they smoke, suffer from lung disease or asthma, or any health problems that limit their activities.

It’s hoped this information will identify who is most at risk by better understanding the COVID-19 symptoms that are linked to health conditions.

Users then answer whether they have been tested for COVID-19 and choose one of two options regarding their health – ‘I feel healthy as normal’ and ‘I’m not feeling quite right’.

The second option takes them through a set of questions, many relating to COVID-19 symptoms – persistent coughing, shortness of breath and fatigue.

Upon completion users are asked to check back in the next day to log another health status update. 

The app was tested using participants from the TwinsUK study – a near-30-year-long scientific study of 15,000 identical and non-identical twins for health research purposes.

Around 5,000 twins and their families across the UK had been recruited from the TwinsUK project to trial the app.

‘Our twins are fantastically committed, enthusiastic health research participants who have already been studied in unprecedented detail, putting us in a unique position to provide vital answers to support the global fight against COVID-19,’ said Professor Spector.