Some of the biomarkers have been linked to PTSD previously, including elevated heart rate [36] and decreased level of coagulation factors [10], and other included markers have been linked to MDD, anxiety, and other comorbid conditions, including platelet volume [43, 44], insulin resistance [41, 49], alterations in the SHANK2 gene [30], and PDE9A expression [31] (Table 2). This evidence concerns the gene SHANK2 and major depressive disorder.