MCOLN1 and mucolipidosis type IV: Loss of function mutations in TRPML1, causes the neurological disease Mucolipidosis Type IV (MLIV) (Sun et al., 2000), and TRPML-associated dysfunction in the endolysosomal system is implicated in other neurodegenerative diseases (Santoni et al., 2020; Lee et al., 2021).