UBE3A and autism: Moreover, in a study investigating the role of the ubiquitin E3 ligase E6AP in autism, it was shown that E6AP expression activates caspase-3 through the inhibition of the X-linked inhibitor of apoptosis (XIAP) responsible for caspase-3 ubiquitination, leading to microtubule cleavage and disorganization of axonal arborization [57].