It has been demonstrated that genetically modified or patient-derived hMOs carrying the G2019S mutation in the LRRK2 gene recapitulated the typical PD phenotype observed in patients with LRRK2-associated sporadic PD, including a reduced number of DA neurons and a lower number of branching, dendrite bifurcations, neurite length, suggesting that there was a significant reduction of the DA neurons network complexity in comparison with the control condition [52,54]. The gene discussed is LRRK2; the disease is Parkinson disease.