For a decade, we commonly prescribed an extremely low dose of amiodarone (50 mg daily) in patients both with and without a history of catheter ablation and systematically measured the serum level of Krebs von den Lungen‐6 (KL‐6) every 3 months for early detection of the possible side effect of interstitial pneumonia (IP). The gene discussed is MUC1; the disease is incontinentia pigmenti.