Finally, we examined whether iN cells can potentially be used to monitor a disease state. We produced a knockdown (KD) of Munc18-1, resulting in a 75% decrease in Munc18-1 mRNA levels (Fig. 5G). Heterozygous loss-of-function mutations of Munc18-1 (gene symbol STXBP1) have been associated not only with severe infantile epileptic encephalopathies (Ohtahara and West syndromes), but also with moderate to severe cognitive impairment and nonsyndromic epilepsy, suggesting that the functions of human neurons are very sensitive to Munc18-1 levels (Pavone et al., 2012). Strikingly, KD of Munc18-1 in human iN cells, such that Munc18-1 levels are decreased but not abolished, led to a major decrease in the frequency but not the amplitude of spontaneous EPSCs, which based on their size probably represent mEPSCs (Fig. 5H). Moreover, KD of Munc18-1 caused a >50% decrease in evoked EPSCs in iN cells (Fig. 5I). Thus, decreasing the Munc18-1 levels in human iN cells produces a major phenotype consistent with the deleterious phenotype observed in heterozygous loss-of-function mutations observed in Ohtahara syndrome.
