Myelin dysfunction in dysmyelinating conditions may be caused by a lack of a particular myelin constituent, e.g., of proteolipid protein 1 in Pelizaeus–Merzbacher disease [5], delay in myelination, as in Allan-Herndon-Dudley syndrome featuring mutations in the SLC16A2 gene that encodes a thyroid hormone transporter [6], or metabolic errors, as in Canavan disease, which is caused by mutations in the ASPA gene encoding aspartoacylase, an enzyme enriched in oligodendrocytes [7]. Here, ASPA is linked to Allan-Herndon-Dudley syndrome.