WARNING: This post contains science and Covid. Those not interested are advised to skip. From: https://www.bbc.com/news/health-54832563 "Covid: Genes hold clues to why some people get severely ill" Briefer version: Why some people with coronavirus have no symptoms and others get extremely ill is one of the pandemic's biggest puzzles. A study in Nature of more than 2,200 intensive care patients has identified specific genes that may hold the answer. They make some people more susceptible to severe Covid-19 symptoms. The findings shed light on where the immune system goes wrong, which could help identify new treatments. These will continue to be needed even though vaccines are being developed, says Dr Kenneth Baillie, a consultant in medicine at the Royal Infirmary in Edinburgh, who led the Genomicc project. "Vaccines should drastically decrease the numbers of covid cases, but it's likely doctors will still be treating the disease in intensive care for a number of years around the world, so there is an urgent need to find new treatments." 'Angry' cells Scientists looked at the DNA of patients in more than 200 intensive care units in UK hospitals ........ to pinpoint any genetic differences, and a number were found - the first in a gene called TYK2. “It is part of the system that makes your immune cells more angry, and more inflammatory,” explained Dr Baillie. But if the gene is faulty, this immune response can go into overdrive, putting patients at risk of damaging lung inflammation. Too little interferon Genetic differences were also found in a gene called DPP9, which plays a role in inflammation, and in a gene called OAS, which helps to stop the virus from making copies of itself. Variations in a gene called IFNAR2 were also identified. IFNAR2 is linked to a potent anti-viral molecule called interferon, which helps to kick-start the immune system as soon as an infection is detected. It’s thought that producing too little interferon can give the virus an early advantage, allowing it to quickly replicate, leading to more severe disease. Interferon can be given as a treatment, but a World Health Organization clinical trial concluded that it did not help very sick patients. However, Prof Jean-Laurent Casanova said the timing was important: "I hope that if given in the first 2-4 days of infection, the interferon would work, because it essentially would provide the molecule that the [patient] does not produce.” But, the Genomicc study - and several others - has revealed a cluster of genes on chromosome 3 strongly linked to severe symptoms. However, the biology underpinning this is not yet understood.