This study reveals new information on the disease mechanisms of a hereditary condition called Mulibrey nanism. Mulibrey nanism occurs if a child inherits a genetic change in a gene called TRIM37 from both parents (recessive inheritance). Children and adults with Mulibrey nanism are shorter than average, they may develop a rare type of heart disease, and their risk of developing tumors is increased. This study describes Mulibrey patients with abnormal numbers of chromosomes in some of their cells. This may be linked to the role of TRIM37 in cell division. Further studies on Mulibrey nanism may help us better understand also other diseases in which similar chromosome changes occur (e.g. cancer). (https://jmg.bmj.com/content/early/2026/02/17/jmg-2025-111325 )