CHRNA4 and schizophrenia: We further examined the relationship between TCF4 bound regions of the genome and histone modifications at specific loci; focusing on TCF4 binding sites that mapped to common variant schizophrenia risk loci discovered by the Psychiatric Genomics Consortium (PGC2).4 We observed 4 TCF4 binding sites that mapped to the CHRNA5/CHRNA3/CHRNB4 locus that encodes subunits of the nicotinic acetylcholine receptor (nAChR) on chromosome 15 (figure 2C).