Diagnosis of

Niemann-Pick Type B

NPB, like NPA, is diagnosed by measuring the acid sphingomylinase (ASM) activity in white blood cells. The test can be performed after taking a small blood sample from individuals suspected of having the disease. While this test will identify persons with Type A (as well as Type B), it is not very reliable for detecting persons who are carriers (who have only one mutated gene).

It is possible to diagnose Type B carriers by DNA testing because the gene containing the blueprint for ASM has been cloned and many of its mutations identified.

The Mount Sinai Department of Human Genetics has identified certain populations* (shown below) where specific mutations account for a high percentage of cases. In other populations, the mutations must first be identified for the affected individual before DNA carrier testing can be performed.

Population                                       Mutation                                 Percentage           

Saudi Arabian                            H421Y, K576N                                  85%

Turkish                                   L137P, fsP189, L549P                         75%

Portuguese/                          S379P, R441X, R474W,                       55%

Brazilian                                               F480L

English/Scottish                                 A196P                                        42%

Other                                                 DeltaR608                                   12%

The Mount Sinai School of Medicine, University of Pittsburgh, and UCSF-Stanford Lysosomal Disease Center can assist with DNA testing and diagnosis for Types A and B.

*From "The Demographics and Distribution of Type B Niemann-Pick Disease: Novel Mutations Lead to New Genotype/Phenotype Correlations" by Simonaro CM, Desnick RJ, McGovern MM, Wasserstein MP, Schuchman EH in the American Journal of Human Genetics, Oct 4, 2002.

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