SPTLC1 and attention deficit-hyperactivity disorder: Notably, regions containing genes encoding key enzymes in the sphingolipid metabolism i.e., serine-palmitoyl transferase (SPTLC1, SPTLC3, SPTSSB) and sphingomyelinases (SMPD1, SMPD4, SMPD3A), have been mapped in association with ADHD (Asherson et al., 2008; Romanos et al., 2008; Rommelse et al., 2008).