Is Mental Illness Hereditary?

Each year, nearly 1 in 5 American adults experiences a mental illness, with half of all lifetime cases beginning by age 14 and 75 percent developing by 24, according to the National Alliance on Mental Illness. And for those who have a known family history of mental health issues, this may lead to the question: “What are my chances of developing a condition?” But the answer isn’t as simple as you might think.

Here’s what you should know about genetics ― and other factors ― when it comes to your mental health.

There’s no specific gene for mental illness, but you can be predisposed.

Scientists haven’t yet found specific genes that can be linked to mental illness. Genetic markers may exist or they may not.

“It’s a complicated picture,” explained Don Mordecai, the national leader for mental health and wellness at Kaiser Permanente. “When we say an illness is ‘genetic,’ really we’re saying that there’s some component of it that is genetic. Of the [conditions] that have been studied so far for genetic markers, there aren’t any where if you have the gene, you have the illness.”

“What we can definitely see is that there is a genetic predisposition. Genetics can increase your risk, but it’s not a guarantee,” Mordecai continued.

In 2013, a study funded by the National Institute of Health found that five mental disorders — autism, attention deficit hyperactivity disorder (ADHD), bipolar disorder, major depression and schizophrenia — share genetic roots. And in 2015, researchers at the University of Wisconsin–Madison studied a family of rhesus monkeys and concluded the risk of developing anxiety is passed from parents to their children. But experts stress more studies need to be conducted in order to come to a more definitive conclusion.

Your environment plays an important role.

What scientists do know definitively is that environmental factors play a significant role in the development of mental health conditions. These include everything from stress to poor nutrition to substance abuse, death, divorce, neglect and family life.

A genetic predisposition to mental illness coupled with environmental factors can increase the chances a child or adult will exhibit symptoms, Mordecai said. He cited a groundbreaking study conducted in the mid-’90s by the U.S. Centers for Disease Control and Prevention and Kaiser Permanente, called the Adverse Childhood Experiences (ACEs) Study. It’s one of the largest investigations of the impact of childhood abuse and neglect on later-life health and well-being, and is “still quite relevant,” he explained.

From 1995 to 1997, researchers surveyed more than 17,000 people about their childhood experiences — including physical, mental and sexual abuse — and their current health status and behaviors.

“What they found was very, very striking — a direct correlation between a number of those events these people had as children and negative health outcomes as a result,” Mordecai explained.

The study showed that as the number of “ACEs” increases, so does the risk of developing a variety of health issues, including mental health conditions like depression or risk of suicide.

Chronic stress and biological factors combined may also play a role.

Another scientific model, known as the stress-diathesis model, attempts to explain the biological relationship between someone’s predisposition for a mental health condition and “major or ongoing stressors,” said Jonathan Sperry, an assistant professor and faculty member in the clinical mental health counseling program at Lynn University. The model says that the combination of chronic stressors like finances, work, academics, marital problems, or health and family issues, and a genetic predisposition to a mental health disorder can actually increase your likelihood of developing a mental illness.

Poverty in particular has been linked to an increased risk of mental illness. Children who grow up poor are more prone to mental illness than their wealthier peers, according to a 2016 paper published in Molecular Psychiatry. Dan Notterman, one of the study’s authors and a molecular biologist at Princeton University, also conducted his own research that found that telomeres — the DNA sequence at the end of certain chromosomes — are shorter in children from poor families, possibly because of stressors like poor nutrition, for example. The shorter telomeres can lead to poor general health.

Even identical twins don’t share the same predisposed risk.

Just because you’re predisposed to a mental health condition and experience an ongoing stressor doesn’t mean you’ll end up with a mental illness, Sperry said. Every person is different ― even twins with similar DNA structure.

“People do respond differently to the same stressor,” Sperry said. “In two twins who have the same genetic DNA, the expression of depression may not happen in one of them. One may not develop the psychiatric disorder that’s in their family tree [even though] they may both go through the same stressor.”

A 2011 study published by King’s College London found that even though identical twins are genetically the same, “non-genetic factors play an important role in the onset of the diseases,” Science Daily reported. The study looked specifically at schizophrenia and bipolar disorder, where heritability is estimated to be 70 percent. Because only one person in each-twin pair had schizophrenia or bipolar disorder, genetic causes were ruled out.

So, what does it all mean?

There’s research that suggests if a family member has a mental illness, your chances of developing it possibly increase, Mordecai said. However, you may never exhibit symptoms if you didn’t experience any traumatic events as a child, your everyday life is relatively stress-free and you’re in a supportive environment.

But it’s also important to note that mental health conditions can develop even if there is no family history. Mental health issues are complex, so it’s vital to recognize the signs like withdrawal, excessive rumination, extreme anxiety, thoughts of self harm, periods of mania and more.

If you think you may have a mental illness, talk with your doctor. Whatever the outcome is, there’s hope. Whether you’re living with a mental illness or think you may be at risk, know that you’re not alone and treatment is available.