The single greatest risk factor, genetic or otherwise, for the development of IPF and RA‐ILD is a gain of function, single nucleotide polymorphism (SNP) in the promoter region of the MUC5B gene (promoter variant rs35705950).52, 53 The wild‐type guanine (G) is switched for the thymidine (T) nucleotide (risk allele). The gene discussed is MUC5B; the disease is idiopathic pulmonary fibrosis.