TOR1A and early-onset generalized limb-onset dystonia: While 15 different gene loci have been implicated in primary hereditary dystonia (DYT1-DYT15) [1], the most common and severe form, early-onset dystonia (also known as DYT1 dystonia) is due to mutation in TOR1A (formerly DYT1) and displays dominant inheritance with reduced penetrance [2].