UBE3A and Ataxia: In this severe disorder, characterized by ataxia and intellectual disability, among other neurological symptoms, the E3 ubiquitin ligase UBE3A/E6AP (E6-associate protein) is nonfunctional due to mutations or deletions in the maternal allele, and concomitant epigenetic silencing of the paternal allele (i.e., parental imprinting) (102–105).