Two to three children in 100 are born with a mental handicap. This can be caused by a genetic defect, but in 80% of the cases scientists do not know which genes are responsible. Now, VIB researchers connected to the Katholieke Universiteit Leuven, in collaboration with an Australian research team, have discovered that, in a portion of these patients, the mental retardation is caused by a twofold production of two proteins (HSD17B10 and HUWE1).