Autism and intellectual disability due to a novel gain-of-function mutation in UBE3A.

The loss of maternal UBE3A causes Angelman syndrome whereas its duplication is associated with a heterogeneous neurodevelopmental disorder. Here, we describe two affected brothers who possess a novel UBE3A variant that is not present in two neurotypical siblings. The UBE3A variant was confirmed to be maternally inherited, and the affected individuals exhibited early global developmental delay, ongoing learning difficulties, and autistic features. Their phenotypes were inconsistent with Angelman syndrome. Biochemical characterization showed the UBE3A variant causes a dramatic increase in the activity of the UBE3A enzyme, suggesting that a gain in UBE3A activity is the driver of neurodevelopmental disease. Our observations document an emerging class of neurodevelopmental disorders caused by gain-of-function mutations in UBE3A.