Thereafter, a least absolute shrinkage and selection operator (LASSO) regression with internal leave-one-out cross-validation and receiver operating characteristic (ROC) analysis identified age and mRNA expression of MUC16, MUC20, and MUC21 as major variables associated with COVID-19 severity (i.e., critically ill or mild COVID-19), with an area under the ROC-curve (AUCROC) of 89.1% and a sensitivity and specificity of 90.0% and 85.7%, respectively (Figure 5A and Supplemental Table 1). This evidence concerns the gene MUC21 and COVID-19.