Explanation:

A new study has found a link between the severity of Covid-19 and a gene linked to dementia. Having a faulty gene linked to dementia doubles the risk of developing severe COVID-19. The gene is called APOE, and exists in a different forms, one of which is termed e4e4. The team found that people with the APOE e4e4 genotype were at double the risk of developing severe Covid-19, compared to those with the common e3e3 form of the APOE gene. APOE (Apolipoprotein E) is a Protein Coding gene. APOE transports lipids, fat-soluble vitamins, and cholesterol into the lymph system and then into the blood. It is implicated in Alzheimer's disease and cardiovascular disease. Hence option 4th is correct.