- Niemann-Pick disease type A and B are clinically but also enzymatically heterogeneous: pitfall in the laboratory diagnosis of sphingomyelinase deficiency associated with the mutation Q292 K. Harzer, K., Rolfs, A., Bauer, P., Zschiesche, M., Mengel, E., Backes, J., Kustermann-Kuhn, B., Bruchelt, G., van Diggelen, O.P., Mayrhofer, H., Krägeloh-Mann, I. Neuropediatrics. (2003)