A dopamine transporter (DaT) scan may be useful to distinguish DOPA-responsive dystonia or rapid-onset dystonia-parkinsonism (where it will be normal) from other causes of parkinsonism with secondary dystonia (Romero-Lopez et al., 2008; Zanotti-Fregonara et al., 2008). This evidence concerns the gene SLC6A3 and Parkinson disease.