NPC1 and 2, which are mutated in Niemann-Pick disease, play a key role in cholesterol trafficking out of the lysosome.17 Cholesterol esters within the lysosomal lumen are hydrolyzed by the LSD-associated protein LIPA (Lipase A), and the cholesterol product is then carried by the lumenal NPC2 protein to the membrane-embedded NPC1 transporter, facilitating cholesterol egress from the lysosome. This evidence concerns the gene LIPA and Niemann-Pick disease.