SMPDL3B and attention deficit-hyperactivity disorder: Combined analysis of SNPs in each gene in the PCG data set and in our study using the Stouffer’s method (which does not correct for markers in LD detected a strong association between ADHD and markers in CERS6 (P < 0.0001), SMPD1 (P = 0.0130), and SMPDL3B (P = 0.0034) from the PGC data set (Supplementary Fig. S1 and Supplementary Table S1).