VMAT1 (SLC18A1) maps to a shared bipolar disorder(BPD)/schizophrenia locus, which is located on chromosome 8p21.  It is thought that disruption in transport of monoamine neurotransmitters due to variation in the VMAT1 gene may be relevant to the etiology of these mental disorders.  One study looked at a population of European descent, examining the genotypes of a bipolar group and a control group.  The study confirmed expression of VMAT1 in the brain at a protein and mRNA level, and found a significant difference between the two groups, suggesting that, at least for people of European descent, variation in the VMAT1 gene may confer susceptibility.  A second study examined a population of Japanese individuals, one group healthy and the other schizophrenic.  This study resulted in mostly inconclusive findings, but some indications that variation in the VMAT1 gene would confer susceptibility to schizophrenia in Japanese women.  While these studies provide some promising insight into the cause of some of the most prevalent mental disorders, it is clear that additional research will be necessary in order to gain a full understanding.