• Overview
• Inheritance
• Symptoms
  • Liver and Spleen
  • Lungs
• Testing
• Treatment
• Resources

Niemann-Pick disease (pronounced "knee-man pick") or NPD affects about 1 in 40,000 people of all ethnic backgrounds. There are at least four types of NPD, called types A, B, C, and D. Types A and B NPD are caused by an absence or shortage of the enzyme acid sphingomyelinase ("ah-sid s-fing-o-my-lin-aze") or ASM, which normally breaks down sphingomyelin ("s-fing-o-my-eh-lin"), a component of cell membranes. This chemical breakdown happens inside of the lysosomes of the body's cells. If the ASM enzyme is absent or in short supply, the sphingomyelin cannot be broken down. Instead, sphingomyelin builds up in the lysosomes of cells in the liver, spleen, and bone marrow. These enlarged cells are called Niemann-Pick cells. The build-up of sphingomyelin results in the symptoms of type A and type B NPD.

Type A NPD is the most common type of NPD and makes up about 85% of all NPD cases. People with type A NPD have onset of the disease in early infancy and undergo progressive brain degeneration, resulting in death usually by age 2 or 3. Failure to thrive (extremely poor growth) and hepatosplenomegaly (enlarged liver and spleen) are also seen in type A NPD.

The symptoms of type B NPD usually appear in infancy or childhood and may vary somewhat from person to person. These symptoms include: enlargement of the liver and spleen, lung disease and susceptibility to lung infections, and occasionally a cherry red spot on the macula (an abnormal red coloration in the center of the retina, the layer of the eye which receives images and transmits them to the brain). Lifespan in people with type B NPD is variable, with many people surviving into adulthood. Type B NPD is sometimes called the non-neuronopathic form of NPD, since (unlike the other types of NPD) it generally does not affect the brain.

Unlike types A and B NPD, type C NPD is NOT caused by mutations in the ASM gene. Type C NPD can be caused by mutations in one of two different genes, called NPC1 and HE1, which are involved in the movement of cholesterol into and out of the body's cells. Symptoms of type C NPD may begin at any time in life, but usually appear during infancy or childhood. Brain degeneration also occurs in this type of NPD, but it is slower than in type A. People with type C NPD may live to adulthood, although death in childhood or adolescence is more common.

The primary focus of this website will be type B NPD, although types A and C NPD will also be discussed.