UBD and COVID-19: PPAR signalling (z-score = − 1.0915; BH p-value = 4.571 × 10–04) and PPARα/RXRα activation (z-score = − 0.302; BH p-value = 3.548 × 10–04) were both downregulated in severe COVID-19, in addition to Antioxidant action of Vitamin C (z-score = − 2.828; BH p-value = 3.548 × 10–02) and FAT10 Cancer Signalling Pathway (z-score = − 1.807; BH p-value = 1.047 × 10–02).