ARSA and metachromatic leukodystrophy: Based on promising pre-clinical results in rodents and non-human primates after intracerebral injection of an AAVrh10-ARSA vector that induced high expression of ARSA in neurons and oligodendrocytes (Piguet et al., 2012; Zerah et al., 2015), a phase 1/2 clinical study of ARSA gene transfer with 12 intracerebral injections to children with early onset forms of MLD was initiated in 2013 (Penati et al., 2017; NCT01801709).