MCOLN1 and mucolipidosis type IV: Mucolipidosis type IV (MLIV) is a lysosomal storage disorder (Lieberman et al., 2012) caused by loss-of-function mutations in the MCOLN1 gene encoding the endolysosomal non-selective cation channel TRPML1 (Bargal et al., 2000; Bassi et al., 2000).