CHRNA5 and schizophrenia: Importantly, CHRNA3 and CHRNB4 are down-regulated (−1.30 and −1.35-fold, respectively) following knockdown of TCF4 in SH-SY5Y cells.41 These data suggest that TCF4 may regulate gene expression at the CHRNA5/CHRNA3/CHRNB4 locus demonstrating a functional association between two distinct schizophrenia risk genes/loci.