How Genetic Is Mental Illness Actually? Heritability Estimates for Mental Health The Role Genes Play

Now, that being said, biological influences do exist, and researchers have been able to study this in two ways: by comparing twins and by researching people that were adopted and raised in a completely different environment than their biological parents. 

So really smart statisticians and researchers have looked at lots of data and estimated how much genetics contribute to mental illness. So that being said, let’s look at the numbers. 

These are the heritability estimates: researchers believe that depression is 30 to 42% heritable, general anxiety disorder around 31%, panic disorder around 43%, schizophrenia between 73 and 90%, bipolar disorder between 60 and 85%, OCD around 47%, ADHD between 60 and 80%. 

Pervasive developmental disorders like autism are around 90% heritable. They’re highly neurodevelopmental. But there is a spectrum of functioning with all disorders. 

Anorexia they estimate between 48 and 88%, and with bulimia 28 to 83%. 

So you can see with these later ones there’s a lot bigger margin of error. They’re not really sure how genes play into those. 

So autism, schizophrenia, bipolar, and ADHD are some of the most heritable disorders, whereas depression and anxiety disorders seem to be influenced more by environmental and psychological factors. 

This does not mean that 42% of your depression is caused by genes and 58% is caused by other factors. It’s way more complex than that. According to the American Journal of Psychiatry, heritability does not really tell you how genetic a disease is but rather how important genes are compared with other risk factors in a given population at a given time. 

So for example, your height is like 90% genetic, but nutrition, injuries, illnesses, cancer on the pituitary gland, etc., these can all impact how tall you grow. And within a single disorder like depression, for example, some forms seem to be more heritable. So if you develop depression at an early age, if it’s recurrent, if it’s more severe, or if you also have an anxiety disorder, your depression is more likely to be genetically influenced. 

So what do we do with this information? Can genetic testing tell you if you have a higher risk? The answer is no, not yet. The genetic influences are just too complicated for our level of science at this point. But maybe one day in the future we will be able to better understand our risks through genetic tests. You can look at your family tree to be more informed. 

But just because another family member has a condition doesn’t mean you will too. So if you have a sibling with depression, your risk of also having it is two to three times greater. If one parent has schizophrenia, your chances of getting it is 10%, but if both parents have schizophrenia then you have a 40% chance of developing the disorder. 

It’s also important to know that predispositions may lower the threshold. They make it so that a certain trigger is more likely to cause bipolar in an individual with that predisposition than in someone else without that predisposition. Genes can turn on traits during the lifespan.