SMPD1 and depressive symptom measurement: In a series of studies, the acid sphingomyelinase–ceramide pathway was shown to play an important role in genetically induced depression (Kornhuber et al., 2014; Müller et al., 2017), mice over-expressing acid sphingomyelinase activity and increased ceramide concentrations showing decreased neurogenesis, neuronal maturation/survival and depression-like behavior (Gulbins et al., 2013).