In addition, many groups found a downregulation of DA markers, such as TH, VMAT2, DAT, and PITX3 both in hMO obtained from idiopathic and LRRK2-associated PD: this observation suggests that at the basis of the PD there is an alteration in the DA neuron development process [52,55]. This evidence concerns the gene SLC6A3 and Parkinson disease.