Chrna6 and Slc6a3 have neural functions related to dopamine: Chrna6 is associated with nicotine dependence but also affects the activity of dopaminergic neurons [49,50,51]; Slc6a3 encodes the dopamine transporter and is involved in multiple neurological conditions ranging from autism to Parkinson’s disease [52]. This evidence concerns the gene SLC6A3 and Parkinson disease.