Twin studies show that genetics plays a role in susceptibility to COVID-19

By Hannah Cueto (Polyplex)

Perhaps you have met two individuals sharing the same physical characteristics to the point you cannot tell them apart? The only thing to differentiate them is how they dress or speak, which they even decide to be on the same terms with.

Identical or monozygotic twins are results of a fertilization of an egg that split into two. Therefore, identical twins share all of their genes with their pair and will always be of the same sex. Meanwhile, fraternal or dizygotic twins result from fertilization of two separate eggs. Compared to identical twins, fraternal twins only share half of their genes with their pair, and they can be of the same or different sexes.

With this information, studying genetic relationships in twins is helpful in improving the field of science, particularly genetics. Recently, a study by Williams et al. of twins in the United Kingdom (UK) shown that susceptibility to COVID-19 symptoms may be inheritable. medRxiv, a preprint server for health sciences, presents the results.

COVID-19 and its symptoms

According to World Health Organization, symptoms of COVID-19 are commonly fever, dry cough, and tiredness, but may also include aches and pains, nasal congestions, headaches, conjunctivitis, sore throat, diarrhea, loss of taste or smell (or anosmia), rashes on skin, or discoloration of fingers or toes.

The researchers used an app in the UK which tracks symptoms such as cough, fever, chest pain, delirium, and anosmia. The participants encoded their symptoms themselves to the application. An individual will be given a “predicted COVID-19” status by observing the age, sex, and symptoms of anosmia, cough, fatigue, and skipped meals that were reported through the app.

The researchers used the data in the app encoded by around 2600 twins from March 25, 2020 to April 3, 2020. These twins are also included in the TwinsUK, an adult twin register in the UK.

 Around 2600 twins included in the TwinsUK, an adult twin register in the UK, encoded their data in the app from March 25, 2020 to April 3, 2020. The researchers then gathered and used their data.

The researchers observed an overall sample of 728 twins with 537 monozygotic pairs and 191 dizygotic pairs, and another sample of 2,104 twins which only included twins living apart.

Results of the study: there is a heritable component

For the overall sample which  has 537 monozygotic twins and 191 dizygotic twins and with 86.9% being female, the researchers claim that the symptoms such as delirium, fever, fatigue, anosmia, shortness of breath, and diarrhea are heritable.

For the sample which only included twins living apart, the study reported that the heritability estimates of fever, anosmia, and shortness of breath are similar with the overall sample. However, there is an increase in heritability estimate for diarrhea while there is a reduction in delirium and fatigue compare to the overall sample.

For predicting COVID-19, there is 50% heritable component in the overall sample while the researchers observed 54% heritable component in the sample, including only twins living apart from each other.

Importance of the twin study in genetics

This new discovery is another step to conquer the unknowns in this novel virus. Determining the factors of genetics that come into play in the virus's spread will help further studies, particularly in public health, to mitigate the effects of the virus, especially on individuals that have higher susceptibility to COVID-19 due to genetic risk.