DefinitionNiemann-Pick disease refers to a group of diseases passed down through families (inherited) in which fatty substances called lipids collect in the cells of the spleen, liver, and brain.There are four most commonly recognized forms of the disease: Types A, B, C, and D. Types A and B are also called Type I. Types C and D are also known as Type II.Each type involves different organs and may or may not involve the central nervous system or respiratory system. Each one can cause different symptoms and may occur at different times throughout life, from infancy to adulthood.Alternative NamesSphingomyelinase deficiencyCauses, incidence, and risk factorsNiemann-Pick disease Type A and B occur when cells in the body lack an enzymecalled acid sphingomyelinase (ASM). ASM helps break down (me