A group of diseases marked by autosomal recessive inheritance and accumulation of sphingomyelin in cells of the RETICULOENDOTHELIAL SYSTEM. They are divided into 5 subtypes: A-E. Type A (classic infantile form) is caused by a deficiency of SPHINGOMYELIN PHOSPHODIESTERASE and presents at age 6-12 months with progressive hepatosplenomegaly and neurologic deterioration. Type B (non-neuronopathic form) presents in childhood with hepatosplenomegaly and pulmonary infiltrates. Type C (chronic neuronopathic form) is caused by defective intracellular cholesterol transport and is divided into severe infantile, late infantile, juvenile, and neonatal hepatitis forms. Type D (Nova Scotian Variant) is phenotypically similar to type C. Type E is an adult non-neuronopathic form. (From Menkes, Textbook of Child Neurology, 5th ed, pp101-4)