SKAP2 and metachromatic leukodystrophy: Deficiency in PSAP or individual SAPs leads to several lysosomal storage disorders including Gaucher disease (Tamargo et al., 2012; Motta et al., 2014), Krabbe disease (Spiegel et al., 2005), and metachromatic leukodystrophy (Matsuda et al., 2001; Kuchar et al., 2009).