Sphingomyelin is a type of sphingolipid that is located in the cell membrane of animals. Sphingomyelin is the only human phospholipid, that does not contain a glycerol residue. Sphingomyelin consists of sphingosine linked by an ester bond to the polar group. The polar group may be represented by phosphocholine or phosphoethanolamine. Due to the amide bond, a fatty acid is attached to the second carbon of sphingosine. Niemann-Pick disease is a hereditary disease caused by impaired lipid metabolism and the accumulation of lipids, in particular sphingomyelin, in the lysosomes of liver, spleen, lung, bone marrow and brain cells. The disease refers to lysosomal storage diseases and is characterized by autosomal recessive inheritance.