MCOLN1 and lysosomal storage disease: Loss-of-function mutations in the human TRPML1 gene MCOLN1 cause mucolipidosis type IV (MLIV) (Bargal et al., 2001; Bassi et al., 2000; Slaugenhaupt, 2002; Sun et al., 2000), a rare recessive lysosomal storage disorder (LSD).