Is Mental Illness Genetic? The Mental Disorders You're Most Likely To Inherit

So it turns out anxiety might be hereditary, according to a new study by the University of Wisconsin-Madison. Young monkeys had their brains scanned when something mildly stressful happened, and then the results were compared to those of their parents and relatives. Guess what? Three different parts of the more anxious baby monkeys' brains lit up in the same pattern as their parents'. These anxious brain reactions appear to have been inherited — but this is only the beginning. A whole lot of mental disorders appear to have strong genetic links.

Finding out whether certain mental disorders can be inherited is massively important, for a lot of reasons. For one, it helps people with those disorders make informed choices about whether they want to have kids. For another, it may help parents understand their kids' behavior early on; for example, being a very anxious child has strong links to serious mental disorders later in life, like depression. It provides answers to sufferers who might feel isolated or bizarre, and it also raises the possibility of a cure — though that's a long way off. 

Many mental disorders may actually have a genetic basis, but we're a significant distance from understanding all the genes involved. These four are the ones with the most research to prove their heredity — but they're by no means the only ones. 

1. Obsessive Compulsive Disorder

Research on the inherited nature of OCD has been around for a while, but the definitive study was in 2000. Researchers looked at OCD sufferers around Baltimore and Washington, and determined that there seemed to be a really strong connection between having an OCD family member (or several) and developing OCD yourself, usually at a young age. 

In 2010 science went further: a study revealed the possible chromosomes that might be responsible for OCD, which — considering that uncontrollable urges and compulsive behaviors cause a lot of problems — may give sufferers who want to have families some hope. But it's more complicated than it seems: OCD may also be caused by environmental factors, and genetics haven't provided all the answers about how or why it appears. So heredity is a part of the picture, but it ain't all of it.

2. Schizophrenia

Schizophrenia is one of the toughest psychiatric problems to diagnose and treat, but it's increasingly believed that there has to be an underlying chemical imbalance in the brain in order for it to develop — and that the imbalance can be inherited from relatives. The numbers don't lie: a parent with schizophrenia gives a child a 40 percent chance of developing it too, even if they aren't in the parent's care, and if your identical twin suffers from it, your chances rise to 50 percent. 

In 2014, there were two breakthroughs about what the genetic inheritance might actually be. There doesn't seem to be a single "schizophrenia gene". Instead, it seems to be a bunch of different genetic problems causing many separate schizophrenic illnesses. One study found eight distinct gene clusters that linked up with eight different types of schizophrenia, while another huge study of 113,000 people found 128 different genetic variants related to schizophrenia. Most had never even been linked to brain problems before. 

And there's something else. A Harvard study in 2014 found a good reason for what goes wrong in schizophrenic brains: the wiring and insulation of nerve fibers aren't working right. Messages are going more awry than paper planes in a tornado. And that, they think, is probably an inherited problem. 

3. Bipolar Disorder

The schizophrenia problem is echoed in bipolar disorder; in fact, those two disorders, plus depression, anxiety and OCD, may actually share some genetic risk factors embedded deep in the genome. But it doesn't seem to be one single gene that can be found and altered to put bipolar disorder out of the picture forever. (That's what "gene therapy" is: tracking down a problem to its genetic source and blitzing it.) Instead, it's considerably more complicated.

Just like with schizophrenia, a chemical imbalance is probably the key here, but a lot of environmental factors seem to contribute to bipolar disorder's appearance as well. Heredity does, however, seem to cast a high risk: having a twin with bipolar disorder increases your own risk of it to 89-93 percent.

Making things more complicated is the fact that there are two kinds of bipolar disorder, I and II. If your family has bipolar II, you're likely to develop either I or II, but for some reason, bipolar I doesn't pass on as much. Researchers aren't sure why.

4. Depression

You probably knew this one: if a close relative is depressed, you're likely to be depressed too. Depression is a huge and multi-faceted disorder with a really strong environmental component, but its genetic component is too big to ignore. The no-single-gene problem rears its head again, but the prevalence of depression among relatives seems to point to one thing: genes are making us sad.

Back in 2011, a huge study seemed to pin down one particular chromosome which might be a trigger for possible depression development: "3p25-26". And around 40 percent of all sufferers who've sought help seem to be able to identify at least one close family member with the same problem. (The number may be even higher; some depressed people don't get any help at all, and others may not realize that relatives have the same condition.)

Overall, though, the picture is complicated: Scientists now think that serious depression may manifest with a few genetic risk factors plus a heap of environmental problems (like stress, grief, or trauma), but they're not willing to bet that a gene might be behind it all. After all, families often share the same stresses and environments, so genes might only be the explanation for why you and all your aunts need therapy. 

So that's the skinny. Blame your genes if you like — they're definitely not innocent — but be warned that if they do eventually create a fix-your-disorder genetic therapy pill, it may not cause everything to melt away to sanity. 

Images: J.K. Califf/Flickr, Giphy

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