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Interpretive Handbook

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Test 8481:
Sphingomyelinase, Fibroblasts

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Niemann-Pick disease (NPD) types A and B result from a deficiency of acid sphingomyelinase, which causes accumulation of sphingomyelin in the organs and tissues of affected individuals. Classification of individuals as having type A or type B is based on age of onset as well as the severity of symptoms. NPD types A and B are inherited in an autosomal recessive manner. Although there is a higher frequency of type A among the Ashkenazi Jewish population, both types are pan-ethnic.

 

NPD type A is a severe neurodegenerative disorder of infancy characterized by failure to thrive, hepatosplenomegaly, interstitial lung disease, neurologic impairment, and regression of developmental milestones typically leading to death by 2 to 3 years of age. All individuals with NPD type A will eventually develop a cherry-red maculae. Bone marrow biopsy will reveal histochemically characteristic Niemann-Pick foam cells.

 

NPD type B is characterized by later onset, milder manifestations, and a much more variable clinical presentation. Most patients are diagnosed in childhood when liver or spleen enlargement is detected during a routine physical examination. Common symptoms include hyperlipidemia and pulmonary involvement. In some cases, severe liver disease is present. Generally, nervous system function and intelligence are normal. Most individuals survive into adulthood.

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of Niemann-Pick disease types A and B

Interpretation Provides information to assist in interpretation of the test results

Deficiency of sphingomyelinase can be demonstrated in cultured skin fibroblasts from patients with the most severe types (types A and B). Values expected in Niemann-Pick disease are <1.0 U/g of cellular protein.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Interfering factors include:

-Lack of viable cells or bacterial contamination

-Failure to transport tissue in an appropriate media

-Excessive transport time

-Exposure of the specimen to temperature extremes (freezing or >30 degrees C)

 

This test is not useful for Niemann-Pick type C detection (see NIEM/9313 Niemann-Pick Type C Detection, Fibroblasts).

 

Level of residual enzyme activity is not a reliable indicator or predictor of severity.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

1.53-7.18 U/g of cellular protein

Clinical References Provides recommendations for further in-depth reading of a clinical nature

1. Gal AE, Brady RO, Hibbert SR, Pentchev PG: A practical chromogenic procedure for the detection of homozygotes and heterozygous carriers of Niemann-Pick disease. N Engl J Med 1975;293:632-636

2. McGovern MM, Schuchman EH: Acid Sphingomyelinase Deficiency, Available from URL: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=npab Reviewed June 25, 2009

3. Schuchman EH: The pathogenesis and treatment of acid sphingomyelinase-deficient Niemann-Pick disease. Int J Clin Pharmacol Ther 2009;47 Suppl 1:S48-57