What causes schizophrenia?

Schizophrenia is a no-fault, equal-opportunity illness most likely caused by a number of factors, both genetic and environmental. Most scientists now accept a two-hit theory for the cause of schizophrenia, which suggests that the genetic susceptibility is compounded by one or more environmental factors:

Genetic susceptibility: Based on family genetic history, some people are more vulnerable to the disorder than other people are.

Environmental factors: In someone genetically predisposed, certain environment factors may come into play, such as:

• Physical trauma that occurs to the fetus during childbirth

• Oxygen-deprivation or some psychological or physical problem that occurs to the mother during pregnancy and affects the developing fetus

• Emotional stress, such as the loss of a parent or loved one during young adulthood.

Although schizophrenia is genetically influenced, more than genetics is involved in its development. Studies of identical twins show that, if one twin develops schizophrenia, the other twin has only a 40 percent to 50 percent chance of also developing the illness. There’s also an increased risk among fraternal twins when one develops schizophrenia, the other has between a 10 percent and 17 percent chance, far less than that of identical twins. Having a parent with schizophrenia also increases a person’s risk of developing the disease, to about 10 percent. And if you have a sibling with the disorder — not your twin — you have a 6 percent to 9 percent chance of developing the disorder yourself.

Scientists still don’t know the precise causes of schizophrenia for any particular individual, yet family members and patients themselves tend to dwell on (or even obsess about) finding a “reason” or a “cause” for the illness. Although this instinct is a natural one, finding the precise cause or explanation is impossible, not to mention counterproductive — finding a reason doesn’t help treatment, and it often creates unnecessary and misplaced guilt, with one family member blaming another.