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Mental illness made the Germanwings co-pilot a victim along with his passengers

It wasn't Andreas Lubitz who flew a plane into a mountain; it was his disease

What are we to make of Andreas Lubitz piloting a Germanwings airplane into the side of a mountain? There is an unhelpful tautology, meant to be explanatory, that arises at times like this. How could someone have done something this evil? Because they were evil. Or: How could someone have done something this heartless? Because they were heartless.

In the case of Lubitz, we have to grapple with the reality of another tautology. As far as can be determined at this time, this sick act was committed by a sick individual with a long history of mental illness. Which puts us into familiar terrain but with a relatively novel twist.

The familiar terrain is of mentally ill individuals with a psychosis acting violently, pummeled by disordered thought, delusions and voices in their heads commanding them to do the unthinkable. This is the world of the likes of John Hinckley, David Berkowitz and Charles Manson, all diagnosed schizophrenics. One pressing challenge with such cases has been to convince the public of the extreme rarity of acts like these — the vast majority of schizophrenics are dangerous only insofar as they break the hearts of loved ones watching the tragedy of a wasted life.

There is no evidence suggesting that Lubitz suffered from schizophrenia. Instead, the novel twist is that his malady appears to have been severe clinical depression. This is the disease in which every cell in the body drowns with groundless anguish, and with suffocating feelings of being hopeless and helpless, in which any attempt to keep despair about the exigencies of life at bay with rationalization fails, replaced with a chest-crushing, metastasized sadness. It appears as if Lubitz had to put his pilot training on hold years earlier because of incapacitating depression, had been taking antidepressants, had a history of suicidal thoughts.

Major depression is enormously dangerous to its sufferers — for example, about 40,000 people commit suicide annually in the United States, and most of those cases involve major depression. But it is immensely rare for depression to result in violence to others.

There are instances of a deeply depressed individual killing his family and then himself. Such an act is usually a mixture of revenge and of a disintegration of ego boundaries, in which it is unclear to the sufferer exactly where he ends and his loved ones begin. Or recall the ghastly tragedy of Andrea Yates, lost in severe, delusional postpartum depression mixed with evangelical Christianity, drowning her five children in the belief that this would guarantee them an eternity in heaven.

It seems unlikely that such scenarios apply to Lubitz — there's no evidence of motivations along those damaged lines; plus, someone mired in that degree of delusional depression would have raised red flags long before settling into a cockpit. Thus, all we have is someone with a history of substantial — and ongoing — depression who has committed an act of mass murder/suicide.

We yearn for explanations, and this does not explain a whole lot. But as we wait for insight that may never come, a few critical things must be remembered, things that mental health professionals would say in their sleep, but which need to be endlessly repeated because they rarely stick.

First, depression, like all mental illness, is an illness, a disease, a situation in which someone's essence has been made unrecognizable by biology gone wrong. Depression is a neurochemical disorder rooted in genetic vulnerability and stressful environmental triggers, in which there are functional abnormalities throughout the brain, in the immune system, endocrine glands, virtually down to the toenails. Depression is as real a biological disorder as juvenile diabetes, and just as no one chooses to have a pancreas that cannot make insulin, no one is able to overcome that little-ol' problem just by showing some gumption. It was not Lubitz who did this; it was his disease. Or to state this as explicitly as possible, the Germanwings crash had 150, not 149, victims.

Second, despite the supreme rarity of Lubitz's manifestations of depression, it is a staggeringly common disease. This is a disease destined to afflict about 1 in every 6 humans at some point in their lives, a disease that, according to the World Health Organization, is closing in on being the second leading cause of medical disability on the planet. Depression is the common cold of psychopathology.

And here is where there is the greatest danger. Mental illness of every stripe is always shrouded in stigma, compromising fair access to employment, housing, healthcare and so on. An untreated major depression is one of the most life-threatening diseases on Earth; if the unprecedented act of Andreas Lubitz drives depression sufferers to hide, deny, ignore their disease even more than is already so often the case, the number of innocent lives lost will dwarf the heartbreaking number of 150.

Robert M. Sapolsky is a professor of biology at Stanford University and of neurology and neurosurgery at Stanford's medical school. He is a contributing writer to Opinion.

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