Genetic mechanisms of critical illness in Covid-19

The subset of patients who develop critical illness in Covid-19 have extensive inflammation affecting the lungs1 and are strikingly different from other patients: immunosuppressive therapy benefits critically-ill patients, but may harm some non-critical cases.2 Since susceptibility to life-threatening infections and immune-mediated diseases are both strongly heritable traits, we reasoned that host genetic variation may identify mechanistic targets for therapeutic development in Covid-19.3 GenOMICC (Genetics Of Mortality In Critical Care, genomicc.org) is a global collaborative study to understand the genetic basis of critical illness. Here we report the results of a genome-wide association study (GWAS) in 2244 critically-ill Covid-19 patients from 208 UK intensive care units (ICUs), representing >95% of all ICU beds. Ancestry-matched controls were drawn from the UK Biobank population study and results were confirmed in GWAS comparisons with two other population control groups: the 100,000 genomes project and Generation Scotland. We identify and replicate three novel genome-wide significant associations, at chr19p13.3 (rs2109069, p = 3.98 x 10-12), within the gene encoding dipeptidyl peptidase 9 (DPP9), at chr12q24.13 (rs10735079, p =1.65 x 10-8) in a gene cluster encoding antiviral restriction enzyme activators (OAS1, OAS2, OAS3), and at chr21q22.1 (rs2236757, p = 4.99 x 10-8) in the interferon receptor gene IFNAR2. Consistent with our focus on extreme disease in younger patients with less comorbidity, we detect a stronger signal at the known 3p21.31 locus than previous studies (rs73064425, p = 4.77 x 10-30). We identify potential targets for repurposing of licensed medications. Using Mendelian randomisation we found evidence in support of a causal link from low expression of IFNAR2, and high expression of TYK2, to life-threatening disease. Transcriptome-wide association in lung tissue revealed that high expression of the monocyte/macrophage chemotactic receptor CCR2 is associated with severe Covid-19. Our results identify robust genetic signals relating to key host antiviral defence mechanisms, and mediators of inflammatory organ damage in Covid-19. Both mechanisms may be amenable to targeted treatment with existing drugs. Large-scale randomised clinical trials will be essential before any change to clinical practice.

Genetic and Phenotypic Evidence for the Causal Relationship Between Aging and COVID-19

Epidemiological studies have revealed that the elderly and those with co-morbidities are most susceptible to COVID-19. To understand the genetic link between aging and the risk of COVID-19, we conducted a multi-instrument Mendelian randomization analysis and found that the genetic variation that leads to a longer lifespan is significantly associated with a lower risk of COVID-19 infection. The odds ratio is 0.32 (95% CI: 0.18 to 0.57; P = 1.3 x 10-4) per additional 10 years of life, and 0.62 (95% CI: 0.51 to 0.77; P = 7.2 x 10-6) per unit higher log odds of surviving to the 90th percentile age. On the other hand, there was no association between COVID-19 susceptibility and healthspan (the lifespan free of the top seven age-related morbidities). To examine the relationship at the phenotypic level, we applied various biological aging clock models and detected an association between the biological age acceleration and future incidence and severity of COVID-19 infection for all subjects as well as for the individuals free of chronic disease. Biological age acceleration was also significantly associated with the risk of death in COVID-19 patients. Our findings suggest a causal relationship between aging and COVID-19, defined by genetic variance, the rate of aging, and the burden of chronic diseases.