TRPML1 was first discovered because its mutations were linked to mucolipidosis type IV (MLIV) (Slaugenhaupt et al., 1999; Bargal et al., 2000; Bassi et al., 2000; Sun et al., 2000), a lysosomal storage disorder (LSD) that impairs neurodevelopment. This evidence concerns the gene MCOLN1 and mucolipidosis type IV.