Strikingly, the TNFα receptor 1 gene TNFR1 was observed as a modifier of CF disease severity as well as of CFTR-mediated residual chloride secretion in the nasal epithelium, whereby the risk and the benign allele were identified consistently for both traits ([13, 40], Figure 1). The gene discussed is TNFRSF1A; the disease is cystic fibrosis.