An Uppsala University-led team links severe COVID-19 risk to loss of chromosome Y (LOY) in white blood cells in men. As they report in Genome Medicine, the researchers used fluorescence-activated cell sorting and droplet-digital PCR to profile LOY in immune-related cells from 211 male patients treated for SARS-CoV-2 infections in intensive care units in Sweden from the spring of 2020 to summer of the following year, analyzing the data alongside available single-cell RNA sequencing data from peripheral blood mononuclear cells from other men treated for severe COVID-19. Their results uncovered relationships between the proportions of white blood cells with LOY, COVID-19 disease severity, and risk of death — associations that were particularly pronounced for infection-related low-density neutrophils (LDN) and other myeloid lineage cells. On the other hand, the proportion of LDN and other cells with LOY appeared to decline in infection survivors in the months following their release from the ICU. "Our results contribute to a better understanding of the importance that LOY has for susceptibility to the disease, especially in relation to the functioning of the immune system," Uppsala University's Jan Dumanski, the study's co-senior and co-corresponding author, says in a statement, noting that the findings "may be relevant to other common viral infections that are more serious for men than for women."