Contributor: Gordon K. Klintworth
Niemann-Pick disease type II is a variant of Niemann-Pick disease. In general this sphingomyelin storage disease is similar to two types of Niemann-Pick disease in the Crocker classification (Niemann-Pick disease type C and Niemann-Pick disease type D). The primary defects in Niemann-Pick disease type II various, but it does not involve a primary defect in sphingomyelinase synthesis. Some patients manifest decreased cholesterol esterification due to a mutation in the NPC1 gene. Sphingomyelin storage is less marked than in Niemann-Pick disease type I. The sphingomyelinase activity in tissue is often normal, but in cultured fibroblasts it ranges from 20-100% of normal.  A diagnosis of Niemann-Pick disease type II by enzyme analyses is uncertain. Niemann-Pick disease type II is subdivided into three groups based on the clinical course of the disease (Niemann-Pick disease type IIA, Niemann-Pick disease type IIS, Niemann-Pick disease type IIC.