Under the definition of Niemann Pick disease (NPD) there are actually many metabolism disorders. At the basis of the pathologies there are specific genetic mutations leading to the deficiency of the basic enzymes. The most common typologies are types A, B and C.
Type A and type B Niemann Pick are related to the abnormal behavior of the sphingomyelinase acid (ASM) enzyme. The enzyme is located within cells called lysosomes and is responsible for metabolizing the sphingomyel lipid. If the enzyme is scarce, the lipid accumulates in the cells and causes death. With time the damage accumulates, with a progressive deterioration of the organs and their functions.
The prognosis for type A and type B of Niemann Pick is very different, despite the basic problem being similar. Type A involves predominantly brain and nervous system, leading to death before the age of 4 years. Type B, however, has almost no neurological implications and allows a much longer life. The bigger problem with Niemann Pick type B sufferers is the enlargement of the organs, which in the long run leads to heart problems.
Type C has a different biochemical and genetic base of types A and B. Those suffering from it can not metabolize cholesterol, which accumulates in the liver. It also fails to metabolize other lipids, which are concentrated in the brain. Sometimes the disease occurs in adulthood, although the first neurological symptoms appear mostly between 4 and 10 years.