What are the recurrence risks for severe nonsyndromic intellectual disability (ID) with one affected first-degree relative?

The selected answer indicates that the recurrence risk for severe nonsyndromic intellectual disability (ID) with one affected first-degree relative, specifically an affected sibling, is estimated at 2-4%. This statistic is grounded in empirical data which shows that having a sibling with severe nonsyndromic ID raises the risk for other siblings compared to the general population.

In families with a history of severe nonsyndromic ID, the observed recurrence risk suggests that although there is an elevated chance of another sibling being affected, it is not as high as one might expect given the single affected sibling. This reflects the complex genetic and environmental contributions to intellectual disabilities in general, where each case may have various underlying factors.

The other options do not accurately reflect the pertinent studies on recurrence risks associated with first-degree relatives. For instance, stating a higher risk than 4% for siblings would be inaccurate according to the data, while a lower risk for parents also reflects a misunderstanding of the study reports surrounding familial recurrence patterns. Understanding these figures is crucial for genetic counselors as they provide essential information to families regarding the potential risks of recurrence in future pregnancies.