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"What if the baby gets one too?," a pregnant friend recently pondered worriedly; nearly everyone in her immediate family has some kind of mental health diagnosis, though the labels they were given are as varied as bipolar disorder, alcoholism, borderline personality disorder, and anxiety. Given the fact that my diagnosis-free friend is the odd one out in her family of origin, it isn't surprising that she is concerned. Even in the absence of official statistics, her lived experience has already taught her that mental illness runs in families — or, at the very least, in hers.
So how likely is it, exactly, that her child will get a mental illness too? Is mental illness really hereditary?
Mental Illness: Nature, Nurture, Or Beyond?
What exactly is "mental illness"? Though we all experience mental health challenges on occasion, a mental illness is a condition that affects someone's thought patterns, behavior, and emotions in a way that adversely impacts their daily functioning — and frequently that of those in their lives — over a long period of time. That's a rather generic definition, and mental illnesses come in all sorts of shapes and forms, with over 200 diagnosable conditions currently recorded. In order to be labeled with a particular mental illness, someone needs to meet a certain number of diagnostic criteria for that illness.
Mental illness, we are aware, "runs in families". Why, though? Even before the complete human genome was mapped, and before we became able to really delve into possible genetic origins of mental illnesses, several possible explanations were being discussed.
- Nature: Indeed, genes that determine whether or not someone will develop a particular mental illness may exist. Research indicates that people whose parents have mental illness are up to 10 times more likely to develop mental illness as well, so the hypothesis that genes could be responsible is not far-fetched.
- Nurture: Another possibility is that mental illness is, instead, the result of nurture. Being raised in an environment where other people have mental illness could mold a person's thinking and behavioral patterns to the point that they, too, qualify for a diagnosis. If mental illness is the result of environmental exposure (and some, like Post Traumatic Stress Disorder, certainly are), then growing up in similarly sub-optimal and stressful circumstances could be the cause of mental illness as well.
- Beyond: Exposure to environmental toxins, including in the womb, may alter a person's brain chemistry to the point that they develop mental illness.
- And yet more: Epigenetics is a relatively new field that investigates how existing genes can be "switched on or turned off" depending on the person's life circumstances, often starting in utero.
These causes aren't necessarily mutually exclusive, and they probably all play a role.