Diagnosis of

Niemann-Pick Type A

NPA, like NPB, is diagnosed by measuring 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 A 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 where specific mutations account for a high percentage of cases.  For NPA, the mutation (R496L, L302P) has a 53% occurrence rate in Ashkenazi Jewish population*.  In other populations, the mutations must first be identified for the affected individual before DNA carrier testing can be performed.

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

*Information from "Identification and expression of a common missense mutation (L302P) in the acid sphingomyelinase gene of Ashkenazi Jewish type A Niemann-Pick disease patients" by Levran O, Desnick RJ, Schuchman EH. Blood, Oct 15, 1992.

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