Finally, multivariate analysis indicates that the predictors of severe COVID-19 (Table 4) also included age above 60 years (HR: 2.65 [1.22–5.77], p = 0.014), presence of diabetes (HR: 2.52 [1.25–5.06], p = 0.009) and high plasma FGF23 levels (HR: 2.12 [1.04–4.28], p = 0.036). This evidence concerns the gene FGF23 and diabetes mellitus.