Histochemical and biochemical observations of the spleen in atypical Niemann-Pick disease and in idiopathic thrombocytopenic purpura.

In a case of adolescent Niemann-Pick disease (NP) and in a case of idiopathic thrombocytopenic purpura (ITP), the histologic picture of the spleen showed appreciable similarity in localization of sparing cells and in a number of histochemical tests. The sphingomyelin, which was the main organ phospholipid in both conditions, contained substantially elevated content of C24 fatty acids. Detailed analysis of spleen lipids showed great relative increase of lysobisphosphatidic acid and of cholesterol which was in NP mainly in free form but in ITP surprisingly mainly esterified, mostly to oleic and palmitic acid. Possible molecular mechanism of sphingomyelin storage was enzymologically followed in model conditions using separated lipid fractions from NP's spleen. The activity of sphingomyelinase (Cl. perfringens exotoxin) was in comparison to phospholipase C relatively specifically inhibited by lysobisphosphatidic acid.