In this highly controlled system of isogenic iN cells, we observed less culture-to-culture variability than the subject cell lines for OPRM1 mRNA and inhibitory neuronal markers (Fig. 2G–I). Moreover, because the patient derived A118 and G118 iN cells exhibited the most robust difference in sIPSC frequency at a DAMGO concentration of 6 ¼M, we examined whether the isogenic iN cells exhibit a similar difference in DAMGO mediated synaptic responses at this DAMGO concentration. We observed a similar decrease in sIPSC frequency compared to subject iN cells following acute DAMGO application, with a stronger inhibition in D40 versus N40 iN cells, and no effect on amplitude (Fig. 2J–O). Furthermore, to determine whether the effect of DAMGO was mediated by the MOR, we applied Naltrexone, a broad spectrum MOR antagonist, and found that the DAMGO-induced synaptic suppression could be reversed (Supplemental Fig. 2J–K). Importantly, administration of Naltrexone alone does not affect synaptic transmission in either genotype (Supplemental Fig. 5). Thus, the reproducibility of the DAMGO response phenotype illustrates that the D40 variant alone explains the differential signaling and the effect is unlikely due to the impact of intrinsic genetic variability between individuals.
