The majority of these genes play critical roles in brain development, such as the NRG1-ErbB4 signaling pathway that is involved in glia cell differentiation, myelination, neuronal migration, axon guidance, synapse formation, and synaptic plasticity; all deficient in schizophrenia (Mei and Xiong, 2008). This evidence concerns the gene NRG1 and schizophrenia.