A Rare Lysosomal Storage Disease

Niemann Pick Type A and B

Sphingomyelinase-activity NPA NPB

Niemann-Pick Types A and B (NPA and NPB), also called Acid Sphingomyelinase Deficiency (ASMD), are caused by the deficiency of a specific enzyme, acid sphingomyelinase (ASM). This enzyme is found in special compartments within cells called lysosomes and is required to metabolize a lipid called sphingomyelin. If ASM is absent or not functioning properly, sphingomyelin cannot be metabolized properly and is accumulated within the cell, eventually causing cell death and the malfunction of major organ systems.

NPA and NPB are both caused by the same enzymatic deficiency and there is a growing evidence that the two forms represent opposite ends of a continuum. People with NPA generally have little or no ASM production (less than 1% of normal) while those with NPB have approximately 10% of the normal level of ASM.

The clinical prognosis for NPA and NPB patients is very different. NPA is a severe neurologic disease that leads to death by 2 to 4 years of age.  In contrast, patients with NPB generally have little or no neurologic involvement and may survive into late childhood or adulthood. Type B individuals usually have enlarged livers and spleens, and respiratory problems are common. The enlargement of organs and the respiratory problems can cause cardiovascular stress and can lead to heart disease later in life.

There are approximately 1,200 cases of NPA and NPB worldwide with the majority being Type B or an intermediate form.

Find additional information here:

– Mount Sinai School of Medicine | Niemann-Pick Type A & B

– Diagnosis of Niemann-Pick Type A

– Diagnosis of Niemann-Pick Type B

Niemann-pick types a and b, or acid sphingomyelinase deficiency (asmd). (2010, June 1). Retrieved from