Nestadt and colleagues found what in their OCD family study?

• A. First-degree relatives of OCD sufferers had an 11.7% risk vs 2.7% in relatives of healthy parents
• B. No difference between groups
• C. OCD is entirely environmental
• D. OCD cannot be inherited

Answer: (A)

OCD showing up more in close relatives points to a genetic contribution to the disorder. Nestadt and colleagues found that first-degree relatives of people with OCD have a higher risk of developing OCD themselves—about 11.7%—compared with relatives of healthy controls, who had about 2.7% risk. This pattern of increased familial risk indicates that genes play a role in susceptibility, even though it’s not the only factor. It also makes clear that OCD isn’t entirely environmental, since relatives share more than just environment; they share genes that raise the likelihood of the condition. At the same time, the risk isn’t 100%, which means other factors—non-shared environment and individual differences—also influence whether someone develops OCD.