Cause or Result in Psychiatric Disorders?

From the introduction of The Harvard Guide to Psychiatry, 3rd edition, Armand Nicholi, MD, says this about the state of psychiatry:

Progress in psychiatry continues in many directions.  More rigorously controlled studies have replaced the relatively unsophisticated research of the past.  Investigators have focused on establishing the neurological substrates of psychiatric disorders--that is, on ascertaining the specific parts of the brain associated with the disturbed thinking, feeling, and behavior of these disorders.  They continue to search for structural, metabolic, and physiological abnormalities that may be clues to the cure of particular illnesses.  And they do so with the full realization that even the identification of such abnormalities will leave unanswered the question of whether they are the cause or the result of the disorder. 

Italics mine.  This last sentence is worth filing away.  Again and again you will be told that specific, identifiable abormalities anatomically or physiologically, say, as seen on an imaging study, give us the cause of this or that condition.  But it just doesn't necessarily follow.