Major depressive disorder is a common mental illness, affecting 19 million adolescents and adults. This disease causes feelings of sadness, emptiness, and loss of interest in things you once enjoyed.

There are many different types of depression and for most of them, genetics can have a huge impact. But environmental factors and lifestyle also determine your risk. Here's what you need to know!

Is depression genetic?
There is no specific gene known to cause depression. Most likely, there are some, or more, genes that if you inherit some of them from your biological parents, they will increase your risk. If you have a depressed parent or sibling, your risk of developing depression is 20% to 30% higher than another normal person, who has a 10% risk. "We know there are genetic factors that seem to be hereditary, but we also know that there are many other factors involved," says Renee Witlen, a psychiatrist in Portland.

Various studies over the years have been a useful method for researchers to investigate how role heredity plays in the development of depression. Inheritance refers to how much your genes account for different traits. Twin studies are often used because identical twins have the same genes, eliminating genes as a variable. A 2009 twin study in the University of Washington Twin Registry estimated the inheritance of depression at 58% among 1,064 twin couples.

Another study of twins in Sweden in 2006 published in the American Journal of Psychiatry found that the inheritance of major depression was 42% in women and 29% in men, indicating that some genetic risk factors may be sex-specific.

Risk Factors for Depression
Witlen says the cause of depression is multifactorial, so while your genes may increase your risk of developing depression, they are not all possible causes. Environmental factors and lifestyle contribute to depression, lifestyle, diet, etc.