Sphingomyelins are the constitutional component of myelin sheath of neuron.In Niemann-Pick Disease,there is accumulation of sphingomyelin in brain, liver & spleen.This accumulation is due to the deficiency of enzyme sphingomyelinase that metabolise sphingomyelins to phosphorylcholine & ceramide. The symptoms of this disease are enlargement of liver & spleen , mental retardation & neurological dysfunction Clinical manifestations are anaemia & Leukocytosis.