It is interesting to note that we only detected evidence for association of NRG genes which are expressed in the central nervous system, namely NRG1, NRG2 and the nervous-system-specific NRG3 [31], whereas NRG4, which is mainly expressed in pancreas and absent from the brain [32] was not found to be associated to schizophrenia. This evidence concerns the gene NRG4 and schizophrenia.