Can Mental Illnesses be Inherited?

July 30, 2018

Can mental illnesses be inherited? Many people have asked this question, especially if they have family who suffers from mental disorders. In addition, a lot of research shows that some mental disorders have a genetic component. 

On the other hand, research hasn’t been able to answer all the questions about how much do our genes influence this. Science advances slowly. Bit by bit, we’re learning more about the genetic inheritance of mental illnesses, although there’s still a lot of ground to cover.

We now understand that mental illnesses and health in general result from both genetics and our environment. In addition, we now know that, in many cases, people don’t inherit the illness itself, just the predisposition to develop it.

People with relatives who suffer from mental disorders often wonder if they may get them.

What factors determine your health?

Getting an illness or not depends on many factors.  This is true even in cases of dominant inheritance. Thus, if there are no predisposing and triggering factors (the spark that lights the genetic fuse), you may never get the disease.

Because of this, scientists use probabilities. It’s impossible to predict if the child of a mentally ill person will develop the same disease. On the other hand, they do have a higher probability of suffering from it. And if the father and mother suffer from the same disease, the probability is even higher.

Let’s discuss the probability of  inheriting some common mental illnesses.

Woman suffering from a possible inherited mental illness.

Likelihood of inheriting schizophrenia

Schizophrenia is a serious mental illness that affects many brain functions, such as thought perception, emotions, and behavior. It’s a psychotic disorder, meaning that those who suffer from it lose contact with reality.

An estimated 1% of the population suffers from schizophrenia. Various studies also estimate that 40% of descendants of a schizophrenic father and mother will develop the disease. 15 out of a 100 people will have psychological anomalies, although not the disease itself.

The incidence rate is the same among fraternal twins. However, among identical twins, one of the twins has an 80% chance of suffering from schizophrenia if their twin suffers from it. It’s caused by a recessive gene, with an incomplete dominance of the carrier gene or genes.

Likelihood of inheriting bipolar disorder

Bipolar disorder is a serious disease due to the associated danger and disability. It’s also known as manic depression. People with bipolar disorder have unusual mood changes. It’s one of the most feared mental illnesses.

People with bipolar disorder have manic episodes and usually feel very happy and lively. They’re also more energetic and active than usual. Other times, people with bipolar disorder suffer depressive episodes and feel very sad and depressed, have little energy, and are much less active than normal.

About 0.4% of the population suffers from bipolar disorder. A patient’s risk increases when their parents suffer from it. Among identical twins, one of the twins has a 95% chance of developing the disorder if their twin suffers from it. It appears to be a dominant gene, with an incomplete dominance of the gene or genes.

Likelihood of inheriting intellectual disability

Most of the serious intellectual disabilities (80%) are caused by environmental factors. It might be an accident or disease that the patient suffered in the womb or in their early childhood. Therefore, they aren’t hereditary.

On the other hand, 80% of mild or moderate intellectual disabilities are linked to inheritance. When both the father and mother have intellectual disabilities, 80% of their children will suffer from the same mental illness. However, only 40% of children will be affected if only the mother or father has an intellectual disability.

A negative factor is that people with intellectual disabilities often form relationships with each other, increasing the chances of a genetic effect. If there’s an inherited gene, it appears to be recessive. It’s possible to inherit a mental illness such as an intellectual disability, although most of them are caused by external factors.

But what about other mental disorders, such as neurosis?

Someone with neurosis reacts abnormally because of previous experiences and environmental causes. Therefore, it isn’t hereditary. Multiple cases of neurosis in the same family can be explained by a “false inheritance”.  It’s not due to genetic inheritance, but instead a poor family environment. This is sometimes called an “emotional pathogen” that tends to trigger the mental illness.

Woman suffering from depression.

That being said, hereditary neurosis has a 70% rate. If a twin has it, their identical twin has an 83% chance of suffering from it as well. However, fraternal twins only have a 23% chance of suffering from the same disorder. Thus, the hypothesis of “emotional pathogen” is still in question.

Neurosis does seem to have a genetic component.  In other words, there seems to be a genetic predisposition to react neurotically to pathogenic experiences. Although some are more likely to be inherited than others, studies on twins and family histories have shown it’s possible to inherit mental illnesses.