Using non-parametric ANCOVA’s to examine group differences in SMase activity levels: a) Controlling for GDS, F(3,116) = 2.91, P = 0.06; aSMase activity in the AD group was significantly lower than both MCI (P = 0.02) and CN (P = 0.04) groups; the MCI and CN groups do not differ from one another (P = 0.6). This evidence concerns the gene SMPD1 and Alzheimer disease.