Figure 5.

Proposed mechanism to explain unexpected positive response of GG individuals to citalopram.

The GG genotype has been postulated to comprise two sets of individuals, those who possess a compensatory mechanism to restore 5-HT signalling, and those who do not. It might be expected that GG individuals without a compensatory mechanism will be prone to depression throughout life and require antidepressant therapy during adulthood. In this study, we propose it is GG individuals who have a compensatory mechanism that present in old age with depression requiring treatment. Due to the downregulation of 5-HT_1A receptors, these individuals may be expected to respond well to SSRI therapy.

G, guanine; SERT, the serotonin transporter; SSRI, serotonin reuptake inhibitor.