In this week’s Medical Discovery News by UTMB’s David Niesel and Norbert Herzog: What makes one person accumulate body fat more than another? For years, scientists believed that the answer to that lay in human genes and their products, but until now, no one knew why or how. At first, they thought mutation of a gene called FTO was responsible. Yet, when they engineered mice with too little or too much FTO, it affected their whole body mass and composition, not just their body fat as is the case with obesity. But since then scientists have discovered that parts of the FTO gene interact with a distant gene called IRX3.