Niemann-Pick type C disease is a rare genetic lysosomal storage disorder that causes severe, progressive neurological symptoms. It is a very serious, life-threatening condition that can affect infants, children and adults. NP-C is characterised by cellular accumulation of lipids, in particular unesterified cholesterol and glycosphingolipids, in many parts of the body including brain, liver and spleen.

The symptoms of NP-C are highly variable and classically present in mid-to-late childhood. Symptoms become progressively more severe and include: disturbance of voluntary rapid eye movements (supranuclear gaze palsy); difficulty in swallowing (dysphagia); slurred and irregular speech (dysarthria); lack of muscle control (ataxia); cognitive dysfunction with associated dementia and in some cases seizures, and sudden muscle weakness during moments of strong emotion such as laughter (gelastic cataplexy). Lipid accumulation can also lead to an enlarged liver and/or spleen (hepatosplenomegaly).

There is currently no cure for NP-C, and until recently, treatments focused only on managing symptoms. These therapies may be at least partially successful in treating some symptoms of NP-C, but have no impact on disease progression or long-term outcomes.