For centuries, we've guessed through anecdotal evidence that some mental health disorders grow strong roots within some families. If one of your first-degree relatives (that's your mom, dad, brother, sister or child) committed suicide, the risk you will (or will attempt to) is four to six times higher than it is for someone in a family without any suicidal behavior in it [source: Landau]. Similarly, if you have a schizophrenic family member, you have an elevated risk for the illness -- in fact, if you have a brother or sister with schizophrenia, your risk of also developing it is 8 times higher than the average Joe, and if you have a schizophrenic parent the risk jumps by 13.8 percent [source: Tsuang].
Is it circumstantial, or are mental illnesses genetic? The quick answer: It's not all a stroke of bad luck. Having just one blood relative with a mental health problem does increase your risk of having one, too. But while mental health professionals consider the genes of your blood relatives to be a factor in whether or not you'll develop mental illness, hereditary factors are just that -- parts of a puzzle. They aren't the only things at play. When you inherit certain genes from your parents, you're predisposed to certain conditions, but your exposure to viruses, alcohol, drugs and other toxins while you were in the womb, as well as your personal biology and brain chemistry, all have a role in your mental health. Experiencing trauma, negative life experiences or living in a high-risk environment are also potential triggers of a psychiatric illness. What we currently know is that while sometimes one, some or all of those factors may catalyze illness, they don't always -- sometimes they increase your risk but never manifest.
Let's take a look at what we know -- and still don't know -- about the genetic roots of mental illness, beginning with a big breakthrough in the late 1980s.