NLGN4X and Parkinson disease: Specifically, CTR and PD patient-derived neurons were differentiated for 2 weeks, replated for 3 days, and then co-cultured with HEK293T cells overexpressing either the post-synaptic molecule NLGN2 (inhibitory synapse) or NLGN4 (excitatory synapse) tagged to the HA epitope, while a plasmid expressing eGFP served as a negative control.