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 are the causes of elevated sm accumulation? Here is an explanation. The disease is a deficiency of neurosphingomyelinase (sphingomyelinase) resulting in impaired metabolism of neurosphingomyelin. It leads to accumulation of the latter in the monocyte-macrophage system, hepatomegaly and splenomegaly, and degenerative changes in the central nervous system. Nerve sphingolipids are formed by linking n-acyl sphingomyelin 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 has the highest activity in normal liver, and liver, kidney and brain small intestine are also rich in this enzyme. In patients with this disease, the activity of the enzyme in the liver and spleen is reduced to less than 50%. In 1914, Niemann reported a case in which the patient died at the age of 18 months, and in 1934, it was discovered that the disease was a neurophosphatidosis, but it was not until 1966 that it was recognized to be due to a deficiency of sphingomyelinase. In the absence of this enzyme, the systemic neurosphingomyelin metabolism is disturbed and neurophospholipids are deposited in the monocyte-macrophage system and in neural tissue cells.