Pectus excavatum (PE) is the most common chest wall deformity, causing a sunken breastbone that can affect breathing and heart function. Most cases occur without a known cause. In our study of 290 children with PE, we discovered that changes in the FBN2 gene—previously linked to a rare syndrome—are surprisingly common among these patients. Using mouse models and genetic analysis, we confirmed that FBN2 defects can directly cause PE-like sternum problems, without other major symptoms. This finding changes how we think about PE: it is not just a mechanical issue but often has a genetic basis. Testing for FBN2 may help families understand their condition and guide future care. (https://jmg.bmj.com/content/early/2026/07/06/jmg-2026-111615)