Importantly, the 5-HT1A G/G genotype is associated with increased 5-HT1A autoreceptors in depressed subjects [179-181], suggesting that 5-HT1A G(-1019) allele is a risk factor for depression by increasing 5-HT1A autoreceptor levels to reduce 5-HT neurotransmission [108,145]. This evidence concerns the gene HTR1A and major depressive disorder.