SMPD1 and attention deficit-hyperactivity disorder: We found an association between ADHD and variants in eight of these genes (GALC, CERS6, SMPD1, SMPDL3B, CERS2, FADS3, ELOVL5, and CERK) in the discovery cohort, with “local replication” for associations with variants in CERS6, SMPD1, and GALC genes.