sphingomyelin

Sphingomyelin is a complex phospholipid belonging to the sphingolipid family, structurally consisting of a sphingosine backbone linked to a fatty acid (forming ceramide) and a phosphocholine head group. It is predominantly found in cell membranes, with highest concentrations in myelin sheaths of neurons, making it crucial for proper nerve conduction. Sphingomyelin is metabolized by the lysosomal enzyme sphingomyelinase (also called acid sphingomyelinase). Genetic deficiencies in sphingomyelinase activity result in Niemann-Pick disease types A and B, autosomal recessive lysosomal storage disorders characterized by progressive accumulation of sphingomyelin in various tissues including liver, spleen, lungs, and brain. Type A presents with severe neurodegeneration and early death, while Type B typically spares the nervous system. The sphingomyelin pathway also plays important roles in cell signaling, apoptosis, and membrane dynamics. Diagnostically, elevated sphingomyelin levels can be measured in tissues or cells, and enzyme activity assays help confirm Niemann-Pick disease.