These few studies, implicating the roles of synaptic plasticity candidate genes BDNF [30] and CREB1 [31], as well as serotonin receptor gene HTR2A [28] and folate pathway gene MTHFD1L [32], have exclusively focused on depression as a relevant disorder, or on depressive symptoms. The gene discussed is MTHFD1L; the disease is depressive symptom measurement.