It has previously been reported that TRPML1 function is essential for lysosomal function (Medina et al., 2015; Settembre et al., 2012; Venkatachalam et al., 2015) and loss-of-function of the channel is implicated in lysosomal storage diseases, such as mucolipidosis type IV (Schmiege et al., 2018). Here, MCOLN1 is linked to mucolipidosis type IV.