Cholesterol is a major component of cell plasma membranes, which define the cell as a whole and its organelles. It is also the basic building block of steroid hormones, including neurosteroids. In Niemann–Pick type C, large amounts of free or unesterified cholesterol accumulate in lysosomes, and leads to relative deficiency of this molecule in multiple membranes and for steroid synthesis. The accumulation of glycosphingolipids in the nervous system has been linked to structural changes, namely ectopic dendritogenesis and meganeurite formation, and has been targeted therapeutically.Several theories have attempted to link the accumulation of cholesterol and glycolipids in the lysosomes with the malfunction of the NPC-1 protein. Neufeld et al. hypothesized that the accumulation of mannose 6-phosphate receptors (MPRs) in the late endosome signals failure of retrograde trafficking of cholesterol via the trans Golgi network. Another theory suggests that the blockage of retrograde cholesterol breakdown in the late endosome is due to decreased membrane elasticity and thus the return vesicles of cholesterol to the trans Golgi Network cannot bud and form. Iouannou, et al. have described similarities between the NPC1 protein and members of the resistance-nodulation-division (RND) family of prokaryotic permeases, suggesting a pumping function for NPC1. Recent 2008 evidence indicates that NPC-1 may play an important role in calcium regulation. Diagnosis
Niemann–Pick type C is diagnosed by assaying cultured fibroblasts for cholesterol esterification and staining for unesterified cholesterol with filipin. The fibroblasts are grown from a small skin biopsy taken from a patient with suspected NPC.
The pregnane X receptor has been identified as a potential target.Neural stem cells have also been investigated in an animal model, and clear evidence of life extension in the mouse model has been shown.Low cholesterol diets are often used, but there is no evidence of efficacy.Gene therapy is being used clinically to treat genetic diseases including haemophilia and spinal muscular atrophy. It has been used preclinically, in a mouse model of Niemann-Pick type C, using an adeno-associated virus derived viral vector has been shown to extend lifespan following injection into the lateral ventricles of the neonatal brain. In a separate proof-of-concept study a similar vector, but with a modified capsid capable of delivering genes to the central nervous system following intravenous injection, was given to Niemann-Pick type C mice at around four weeks of age; this resulted in extended lifespan and improved weight gain. Prognosis
The lifespan of patients with NPC is usually related to the age of onset. Children with antenatal or infantile onset usually succumb in the first few months or years of life, whereas adolescent and adult onset forms of Niemann–Pick type C have a more insidious onset and slower progression, and affected individuals may survive to the seventh decade. Adult cases of NPC are being recognized with increasing frequency. It is suspected that many patients affected by NPC are undiagnosed, owing to lack of awareness of the disease and the absence of readily available screening or diagnostic tests. For the same reasons the diagnosis is often delayed by many years.