A novel conditional knock-in approach defines molecular and circuit effects of the DYT1 dystonia mutation

DYT1 dystonia, the most common inherited form of primary dystonia, is a neurodevelopmental disease caused by a dominant mutation in TOR1A. This mutation ('δE') removes a single glutamic acid from the encoded protein, torsinA. The effects of this mutation, at the molecular and circuit levels, and the reasons for its neurodevelopmental onset, remain incompletely understood. To uniquely address key questions of disease pathogenesis,we generated a conditional Tor1a knock-in allele that is converted from wild-type to DYT1 mutant ('induced' δE: Tor1a^i-δE), following Cre recombination.We used this model to perform a gene dosage study exploring the effects of the δE mutation at the molecular, neuropathological and organismal levels. These analyses demonstrated that δE-torsinA is a hypomorphic allele and showed no evidence for any gain-of-function toxic properties. The unique capabilities of this model also enabled us to test a circuit-level hypothesis of DYT1 dystonia, which predicts that expression of the DYT1 genotype (Tor1a^δE/+) selectively within hindbrain structures will produce an overtly dystonic animal. In contrast to this prediction, we find no effect of this anatomic-specific expression of the DYT1 genotype, a finding that has important implications for the interpretation of the human and mouse diffusion tensor-imaging studies upon which it is based. These studies advance understanding of the molecular effects of the δE mutation, challenge current concepts of the circuit dysfunction that characterize the disease and establish a powerful tool that will be valuable for future studies of disease pathophysiology.