Rare variants appear to be implicated in 10%−30% of cases of autism spectrum disorder and up to 3%−5% of cases of bipolar illness and schizophrenia.39 When present, they may be associated with specific medical syndromes.13 If present in the parents, they also may be associated with an increased risk for illness in siblings. Psychiatrists should be aware of the substantial risk that some rare variants confer, when and how to test for them, and the implications of these variants on clinical management of psychiatric conditions.
