SM accumulation is 4 to 6 times normal and enzyme activity is normal. Niemaoh-Pick disease (NPD), also known as sphingomyelin lipidosis, is a congenital disorder of glycolipid metabolism. It presents with elevated accumulation of serum mucin (SM). Niemann-Pick disease is characterized by a large number of foamy cells containing neurosphingomyelin in all mononuclear macrophages and in the nervous system. It is less common than Gaucher’s disease. It is autosomal recessive and is more prevalent in Jews with a prevalence of 1 in 25,000. there are at least five types. So what is the pathogenesis of elevated sm accumulation? Here is an explanation. Pathogenesis The disease is a disorder of nerve sphingomyelin metabolism caused by a deficiency of sphingomyelinase. The latter accumulates in the monocyte0macrophage system, resulting in hepatomegaly, splenomegaly, and degenerative lesions of the central nervous system. Nerve sphingolipids are formed by linking N-acyl sphingosine with a molecule of phosphocholine at the C1, site. Neurosphingolipids are derived from various cell membranes and the erythrocyte matrix, among others. After phagocytosis by macrophages during cellular metabolic senescence. This enzyme is most active in the normal liver and is also abundant in the liver, kidney and brain small intestine. In patients with this disease, the activity of the enzyme is reduced to less than 50% in liver and spleen tissues. Large, lipid-rich foam cells, 20 to 90 μm in diameter, are found in the reticuloendothelial system of the child, mainly in the spleen, bone marrow, liver, lungs, and lymph nodes. These foamy cells, also known as Niemann-Pick cells, usually have only a small, off-set nucleus with loose chromatin; the cytoplasm is filled with lipid droplets (cytoplasmic bodies) and appears “mulberry”-like on unstained slices, and when stained with Giemsa, the cytoplasm is blue or blue-green with shades of blue granules. Unlike Gaucher cells, acid phosphatase staining is weakly positive and Schultz reaction (for cholesterol) is positive. The two can also be distinguished by bitemporal microscopy or electron microscopy.