Lymphocyte enzymes in the detection of Niemann-Pick Carriers

An improved method for the detection of Niemann-Pick disease type A and B carriers is described. Niemann-Pick disease is a genetic disorder characterized by the accumulation of sphingomyelin in several organs, among them spleen, liver and brain. A deficiency in sphingomyelinase activity is the characteristic defect in this lipid storage disorder, and the decreased enzyme activity in these types can be demonstrated in various cells and tissues. Low activity levels of enzymes were found in leukocyte fractions of peripheral blood from patients screened for Niemann-Pick disease. In heterozygote patients levels were within the lower range of control values. We therefore determined sphingomyelinase activity in discrete cell types isolated by two different methods from the total leukocyte fraction. In normal subjects sphingomyelinase activity is five to ten-fold higher in lymphocytes than in granulocytes. Monocytes have an intermediate level. pH profile and stability to heat inactivation were tested in separated lymphocytes and granulocytes and were found to be insignificantly different. Detection of carriers for Niemann-Pick type A and B by using separated lymphocyte as enzyme source, overcomes the difficulty of overlapping values with normal controls and serves as an excellent tool to detect heterozygotes.