Information for Health Care Providers - NPD Type A
An Excellent Summary of Information about Acid Sphingomyelinase Deficiency (Niemann-Pick Disease, types A, A/B and B) can be found by selecting the link below to the GeneReviews section of the GeneTest resource for healthcare providers. This is an NIH-funded resource on clinical and research genetic testing.
Inheritance
All types of NPD are inherited in an autosomal recessive pattern and can affect both males and females. The disease occurs when both copies of a person's acid sphingomyelinase gene have a mutation (a change in a gene which causes it to function incorrectly). Carriers have one normally functioning copy of the gene and one copy that does not function correctly due to a mutation; carriers do NOT have NPD. Being a carrier of NPD is not known to lead to any health problems. Far fewer than 1% of people in the general population are Type A NPD carriers, however, among Eastern European Jews, 1 out of 90 individuals is a carrier for Type A NPD.
A person with NPD inherits one gene mutation from each parent, both of whom are carriers. Each child of two carrier parents has: a 25% chance of being unaffected and not a carrier (having two working copies of the gene), a 50% chance of being an NPD carrier (having one functional copy and one non-functional copy, like his/her parents), and a 25% chance of having NPD (having no working copies of the gene).
Blood relatives (siblings, aunts/uncles, cousins, etc.) of patients with NPD may also be carriers of an NPD gene mutation. If the mutations in the affected family member are known, definitive carrier testing can be done for these relatives.
The different details of each family history will cause the risk figures and other genetic conseling issues to vary from family to family. For example, if there is a family history of Type B NPD for one partner and the other partner is identified as a carrier for Type A, there would be a risk for having a child with an intermediate variant of the conditions caused by acid sphingomyelinase deficiency. Genetic counseling is recommended for all couples in which both partners are known to be carriers, or if one partner is known to be a carrier and the other's status is uncertain.
Updated 3/30/2010, CWV