ASPA and Cowden disease: Canavan disease (CD) is a rare monogenic neurodevelopmental disorder caused by autosomal recessive loss-of-function mutations in the ASPA gene encoding aspartoacylase (ASPA).1 ASPA is expressed by oligodendrocytes in the central nervous system (CNS) where it hydrolyzes N-acetylaspartate (NAA), its only known substrate, into acetate and aspartate.1,2 No other enzyme is known to hydrolyze NAA and the high levels of NAA observed in CD are considered pathognomonic.1