The New York Times’ Gina Kolata reports today on a study in Science that researchers at Boston Children’s Hospital have made an important finding in the obesity genetic puzzle. Scientists have known for a long time that a person’s genetic inheritance influences their body weight. Studies of twins in controlled laboratory settings showed a significant range in how much weight a twin gained. Now comes a possible explanation. The team led by Dr. Joseph Majzoub found a gene, MRAP2, acts as a helper gene to signal another gene which controls appetite. When they removed the gene, animals doubled their weight. The only way these mice could remain slim was to be fed about 10-15% less than their siblings with the gene. In mouse-adolescence, they were ok. But as adults, they developed great appetites.