The only gene that has been tested previously for association with traits relevant to our study was the SYNJ1 gene. It is a phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2) involved in clathrin-coated pit dynamics, which are required for efficient synaptic vesicle endocytosis and re-availability at nerve terminals [37]. It was identified in a linkage region for bipolar disorder, but the association analysis results of this gene with depression have been inconsistent. Stopkova and colleagues [38] did not find differences in allele frequencies between controls and bipolar patients for a common mutation, and previous rare variants in this gene were not detected in their sample. However, one of the homozygote groups was overrepresented among bipolar patients in one of their samples. In our study, no SNPs in SYNJ1 were associated with depression or associated measures of anxiety and neuroticism, suggesting that the effects of this gene on depression may be limited to rare mutations if they are important at all.
