UBE3A mutations (11% of cases) – In these individuals, mutations in the UBE3A gene prevent its expression or function. Thus these individuals do not have the appropriate levels of functional UBE3A in the brain.
(UPD; 7% of cases) – in UPD, the individual has two copies of paternal Chromosome 15. Because UBE3A is not expressed from the paternal copy, these individuals lack normal levels of UBE3A in the brain.