Should the diagnosis of major depression be made independent of or dependent upon the psychosocial context?

BACKGROUND: The diagnosis of certain psychiatric syndromes (e.g. panic attacks, post-traumatic stress disorder) is crucially dependent on the psychosocial context in which they arise. For other syndromes (e.g. schizophrenia), the context is generally irrelevant. Should the diagnosis of major depression (MD) be made dependent upon or independent of the psychosocial context in which it occurs?
METHOD: Twins were selected from a population-based registry who, on personal interview, reported developing a full depressive syndrome either 'out of the blue' or in response to stressful life events (SLEs) rated objectively as having mild, low moderate, high moderate or severe long-term contextual threat (LTCT).
RESULTS: In these depressed subjects, no relationship was found between the level of adversity associated with onset and most indices of liability to depression, including risk of MD in co-twin and parents, level of neuroticism, risk for future depressive episodes, co-morbidity with other internalizing disorders and history of sexual abuse. Compared to the remainder of this epidemiologic cohort, subjects developing depression in response to the severe threat events had substantially elevated levels of all the examined indices of liability to MD.
CONCLUSIONS: Individuals who develop a full depressive syndrome in response to high-threat events do not have an appreciably lower liability to MD than those developing depression after exposure to low adversity and have much higher liability to depression than observed in their population cohort. These results support the hypothesis that, in general, MD can be diagnosed independently of the psychosocial context in which it arises.