The issue focused on genes associated with cognition and psychiatric disorders has prompted extensive scientific inquiry into genetic markers for schizophrenia and bipolar disorder. Recent publications describe associations between dopamine transporter genes (DRD4 and DRD5), chromosome regions containing NRXN1 (chromosome 13q21–22), genes encoding neurotransmitter receptors (NRXN2 and NRXN3), genes encoding neurotrophic factors (NF1 and NF2), proteins associated with synaptic transmission (NRXN4), proteins associated with synaptic morphology