Niemann–Pick disease is a group of severe inherited metabolic disorders, in which sphingomyelin accumulates in lysosomes in cells (the lysosomes normally transport material through and out of cells). These disorders involve the dysfunctional metabolism of sphingolipids, which are fats found in cell membranes (so it is a kind of sphingolipidosis, which is included in the larger family of lysosomal storage diseases). [Source: Wikipedia ]