Genetic Factor of Schizophrenia

Based on evidence from large demographic studies, schizophrenia appears to have a strong genetic component. For example:

• People with one affected first-degree relative (e.g., one parent) have a 10% higher risk for developing schizophrenia.
• In children with two affected parents, risk is increased by 40%.

In addition, schizophrenia is more likely to occur in both members of identical (monozygotic) twins than in both members of nonidentical (dizygotic) twins. This is significant because identical twins have the same genetic profile, whereas the genetic similarity between nonidentical twins is the same as among nontwin siblings. Specifically:

• When one identical twin has schizophrenia, the other has a 40% to 50% chance of being affected.
• When one nonidentical twin has schizophrenia, the other has only a 10% chance of being affected. It is important to note that when one identical twin has schizophrenia, the second twin does not have a 100% chance of being affected. This means that the development of schizophrenia cannot be solely attributed to genetic factors.

Despite the evidence that genetic factors play a role in the etiology of schizophrenia, it remains unclear how these factors influence development of the disease. In fact, the ereditary aspects of schizophrenia are probably the result of a complex interplay among different genes or subsets of genes, rather than through individual genes.