“…The study revealed that 3 in 1,000 individuals with MDD carried expanded HTT CAG alleles [99]. Alterations of serotonergic brain stem raphe were associated with a depressive state in patients with HD [100]. Another study found that female-specific depression phenotype R6/1 transgenic HD mice had decreased serotonin and serotonin metabolite levels in the brain and consequent alterations in 5-HT 1A receptor signaling [101].…”