Regarding the genetics of schizophrenia, the concordance rate for schizophrenia in monozygotic twins of affected probands is approximately:
- A 10 percent
- B 25 percent
- C 50 percent ✓
- D 90 percent
Correct answer: C. 50 percent
Explanation
Twin studies consistently show monozygotic concordance of about 50 percent compared with roughly 10 to 15 percent in dizygotic twins, demonstrating a strong genetic contribution while confirming that genes alone are insufficient and environmental factors are necessary. The general population lifetime risk is about 1 percent, rising to about 10 percent in first-degree relatives. Concordance below 50 percent would underestimate the well-replicated twin data.
Reference: Kaplan and Sadock's Synopsis of Psychiatry, 12th ed.
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