GCH1 and Dystonia: Thus, torsin acts as a positive regulator of GTP cyclohydrolase (DYT5a) in Drosophila. While studies currently in progress are aimed at identifying the underlying molecular mechanism of this interaction, these results provide evidence of a normal cellular function for the torsin protein, as well as an intriguing functional connection between the genes associated with DYT1 and DYT5 dystonias.