Is Schizophrenia Hereditary? Not as Much as We Thought

Most people with a sibling or parent with schizophrenia will not develop it.

Posted Jun 18, 2018

Schizophrenia is a severe psychotic disorder that affects about 1 percent of the population.

Is schizophrenia hereditary? Although it clearly runs in families, most people with a relative or even a sibling or parent with schizophrenia will not develop the disorder. The other piece of good news is that the estimates of how heritable it is are declining.

Over the years, researchers have found that the chance of one twin suffering from schizophrenia if the other did was anywhere from 44 to 87 percent. The most common figure cited was 81 percent.

And a 2012 analysis of records for all people in Denmark found that the chance of suffering from schizophrenia if a parent did was 67 percent.

However, the risk may be lower. A 2014 report from the Consortium on the Genetics of Schizophrenia Family Study in the United States with nearly 300 families concluded that the risk of schizophrenia was only 31 percent within a nuclear family. The group’s strategy is to identify endophenotypes—specific symptoms linked to genes. In 2014 the group announced that it had found 12 of these markers. In 2016, it reported on another 13.

Linking symptoms to genes is essential because the symptoms can be very different from one patient to another, with different genes, as well as other factors, at play.     

Most people begin displaying symptoms in their late teens or early twenties, but in some cases, the signs appear in the forties or later. In those patients, one study indicates, the family history of illness was weaker. The patients were more likely to be female and to have other illnesses and stresses like a history of unemployment.

Most likely, several small variations in genes combine to increase the risk of symptoms. Scientists know that experiences like infections in the womb or stress during childhood affect the outcome.

For example, a child with a family history of schizophrenia who is also neglected is more likely to become apathetic, losing interest in her usual activities and possibly end up in bed for much of the day. If she’s not neglected, she might hear voices and show other symptoms but not become apathetic.

A small deletion in a region of chromosome 22 called 22q11 seems to contribute to a small percentage of cases; these patients may also have problems with their heart and immune system and cleft palate.

What are the symptoms of schizophrenia? Some people hear voices, or they may hallucinate visions, smells, or tactile sensations. They may also hold delusions. A person with schizophrenia might believe he is Jesus or that he’s being controlled by aliens.

Substance abuse, suicidal thoughts, and attempts of suicide are more common in this group than the general public.

People with schizophrenia sometimes become “flat”—with few facial expressions—or even completely unresponsive. They may develop movement problems, sometimes as a side-effect of medication. They may also have depression and bipolar disorder and be diagnosed with schizoaffective disorder.

Family members of people with schizophrenia can get information and support through the National Alliance on Mental Illness and online forums.

A version of this story appears on Your Care Everywhere.