Indeed, previous studies have shown different efficiencies in the hydroxylation of steroid hormones depending on the allelic variants on the CYP1A1 gene, resulting in changes in its catalytic efficiency.33 Our two patients with the CYP1A1 gene mutation had a GCC‐induced osteoporosis related to chronic obstructive pulmonary disease and rheumatoid arthritis, respectively, with previous fragility fractures and were also receiving treatment with BPs prior to developing the fracture. Here, CYP1A1 is linked to rheumatoid arthritis.