One possible cause of schizophrenia — or an important contributing factor — may be heredity, or genetics. Researchers believe that some people may inherit a tendency to be at greater risk for schizophrenia in their lifetime. In fact, the disorder tends to run in families — but only among blood relatives.

Genetics and genetic mutations play an important role in the cause of many mental illnesses. What exactly that role is and the extent to which a certain mutation results in a greater risk factor varies widely. We simply do not yet know exactly what causes mental illnesses like schizophrenia. But it’s clear there’s an important role that genetics plays.

People who have family members with schizophrenia may be more likely to get the disorder themselves. If both biologic parents have schizophrenia, there is nearly a 40 percent chance that their child will get it, too. This happens even if the child is adopted and raised by mentally healthy adults. In people who have an identical twin with schizophrenia, the chance of schizophrenia developing rises to nearly 50 percent.

In contrast, children whose biological parents are mentally healthy-even if their adoptive parents have schizophrenia-have about a 1% chance of getting the disease. That is about the same risk as for the general population shown in the chart.

Chances of Developing Schizophrenia

  • General population: 1%
  • Brother or sister has schizophrenia: 8%
  • One parent has schizophrenia: 12%
  • Fraternal twin has schizophrenia: 14%
  • Both parents have schizophrenia: 39%
  • Identical twin has schizophrenia: 47%

Schizophrenia is not passed on directly, like eye or hair color. Other conditions — not yet fully understood by researcher — are necessary because other factors are involved. Otherwise, schizophrenia would always develop in both identical twins, since they have the same heredity.

The causes of schizophrenia — like all mental illness — are complex and multi-factored. Anybody who says, “Schizophrenia is a genetic disease” is simplifying our understanding of this condition to the point of meaninglessness. Certainly genetics is an important part of the puzzle, but it alone does not explain the emergence of the disorder in some people with a certain set of genetic components, while it remains at bay in others.