The Niemann-Pick C2 (NPC2) gene encodes a 151-amino acid glycoprotein located inside the lysosomes and it is mainly involved in transferring cholesterol and other lipids from the lysosomes to other parts of the cell. This glycoprotein is produced in all tissues, however, high levels are found in epididymal fluid as well as in testis, kidney, and liver. Mutant NPC2 gene is responsible for causing about 5% of all cases with Niemann-Pick disease type C (NPC). Mutations in the gene cause an abnormal lipid buildup in the cells leading to abnormal cell function. Infant or juvenile onset of NPC disease is usually caused by mutations that either prevent glycoprotein formation or radically shorten it. On the other hand, alteration of only one amino acid enables the glycoprotein to retain some of its function causing a less severe, more slowly progressing NPC disease.