Last Updated on June 3, 2023

The jury is still out on how much is nature or nurture, genetics or environment when it comes to what trips mental illness. Two psychiatric conditions that have been closely linked to heredity are bipolar disorder and schizophrenia. Depression as well as other types of mental illness also have a tendency to run in families. When it comes to nature versus nurture bu, we have a lot to understand.

“Most mental illness is most likely due to some combination of inheritance and exposure,” says Vishwajit Nimgaonkar, MD, a psychiatrist at the University of Pittsburgh Medical Center who focuses on genetics. “When we started to map the human genome 25 years past, we thought we might find the solution to psychiatric illness in our genetic code. Regrettably, a straightforward genetic cause has not been found.”

Inheriting Bipolar Disorder, Schizophrenia, and Depression

“The best evidence for familial mental disease is in schizophrenia and bipolar disorder. If both your parents have either one of the psychiatric problems, you may have a 40 to 50 percent risk of inheriting the condition,” says Edwin Meresh, MD, assistant professor of psychiatry in the Loyola University Health System in Chicago.

Schizophrenia is a mental illness characterized by disorganized thoughts and feelings; it’s also possible to experience a disconnect from reality. Bipolar disorder is characterized by mood swings between depression and hyper-excitability, called mania. Depression is more than feeling blue; it is despair and a deep seeded sorrow.

Here’s what we understand:

• Schizophrenia affects about 1 percent of the people. If one of your parents has schizophrenia, your chance of getting the ailment is 13 percent. The risk of developing schizophrenia goes up with each additional family member that has got the disease.

• Bipolar disorder affects about 2 to 3 percent of the population. If one of your parents has bipolar disorder, your chance of getting the disease is 15 percent. The risk of developing bipolar disorder also goes up with each additional family member which has the disease.

• Major depression affects about 10 percent of the population. If one of your parents or a sibling has major depression, your risk increases by 20 to 30 percent.

The
Genetics of Mental Illness

That’s not true for mental illness, although a single abnormal gene causes some diseases. “There are lots of genes that have been identified. We are discovering genetic variations that are large, so there are likely distinct things that trigger those genes and multiple genes. We suppose that schizophrenia is all about 75 percent genetic, but we have only been able to find 5 to 10 percent of those genes so far,” says Dr. Nimgaonkar.

Studies on twins reveal that genes don’t tell the entire story. “If it was all genetic, you’d expect that identical twins, who share exactly the same genes, would also possess the same mental illness. But even if one identical twin has schizophrenia, the other twin just has the ailment about 50 percent of that time period,” says Dr. Meresh.

Researchers in over 20 countries have been participating in a genetic study of mental illness called the Psychiatric Genome-Wide Association Study Consortium. So far, they’ve examined the genomes (an individual’s complete genetic code) of more than 50,00 people with mental illness. They recently released some of the findings in the journal Nature Genetics. This is exactly what they found:

• Gene variations that are common lead to both schizophrenia and bipolar disorder.
• There are at least 11 regions of the genome that are firmly connected with both diseases.
• Neither disease is caused by a single gene, but by a combination of several genes and unidentified non-genetic variables.

“It’s also crucial that you know that even if you don’t inherit a gene for mental illness, you can still have a genetic cause. Genes can change after arrival and lead to mental illness. This really is called a de novo genetic change,” says Nimgaonkar.

Non-Genetic Reasons For Mental Illness

What are the other causes if mental illness is just not all genetic? That’s another place that we have to understand more about. Here are just a few of the non-genetic chances:

• Complications during pregnancy
• Drug abuse
• Stress
• Injury early in life
• Surviving in a dysfunctional house
• Physical or sexual maltreatment
• Parental disregard
• Losing a parent early in life

“As we learn more about the genetic and non-genetic reasons for mental illness, we might manage to target drug treatment more successfully. One day, we may be able to do a blood test that will predict or diagnose mental illness, but we’re not there yet,” says Nimgaonkar.

We all know that something in the surroundings must also be demanded to trigger a psychiatric issue and that genes are not the whole narrative. So that the age-old debate of nature versus nurture goes on. The answer appears to be someplace in the middle.