ACP2 and mucolipidosis: The processing of other integral lysosomal membrane proteins, such as the lysosomal acid phosphatase Battenin (encoded by the gene CLN3, which causes neuronal ceroid lipofuscinoses when mutated) or the mucolipin subfamily of transient receptor potential proteins (TRPMLs, mucolipidosis-associated) is in many aspects similar to cystinosin-LKG, involving passage through the plasma membrane [24–26].