Figure 2

Pathophysiological pathways to early-onset depressive disorders. There are at least three common trajectories that lead to depression in the teenage and early-adult years. These are characterized by (1) ‘anxiety-central nervous system reactivity’, (2) ‘circadian and 24-hour sleep-wake cycle dysfunction’, and (3) ‘developmental brain abnormalities’. The six corresponding phenotypic patterns have distinct ages of onset and characteristics. From age 8 to 10 years onwards these processes are transformed by key neurobiological phenomena: (a) puberty, (b) adolescent brain development, and (c) sleep-wake cycle [see [122].