ARFGEF2 and post-traumatic stress disorder: For example, the top lead SNP (rs67777906; P = 1.80 × 10−15) is situated in the ARFGEF2 gene, implicated in both bipolar disorder (BD) and schizophrenia but showing opposite directions of effect and hence may be a marker that could be used to differentiate between the two [20], as well as being linked to post-traumatic stress disorder (PTSD) [21, 22].