Two meta-analyses of overlapping studies examining the 5-HT<sub>1A</sub> receptor (largest n = 561), and three meta-analyses of overlapping studies examining SERT binding (largest n = 1845) showed weak and inconsistent evidence of reduced binding in some areas, which would be consistent with increased synaptic availability of serotonin in people with depression, if this was the original, causal abnormaly. Here, SLC6A4 is linked to depressive symptom measurement.