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Interpretive Handbook

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Test 62235 :
Psychosine, Blood Spot

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

Krabbe disease (globoid cell leukodystrophy) is an autosomal recessive lysosomal storage disorder caused by an enzyme deficiency of galctocerebrosidase (GALC). Krabbe disease is caused by mutations in the GALC gene, and it has an estimated frequency of 1 in 100,000 births.

 

Patients typically present before the first year of life with central nervous system impairment with increasing irritability and sensitivity to stimuli. Rapid neurodegeneration including white matter disease follows with death usually occurring by age 2. A small subset of individuals have late onset forms of the disease that are characterized by ataxia, vision loss, weakness, and psychomotor regression presenting anywhere from age 6 months to the seventh decade of life. The clinical course of Krabbe disease can be variable, even within the same family. Treatment is mostly supportive, although hematopoietic stem cell transplantation has shown some success if treatment begins before neurologic damage has occurred.

 

Reduced or absent galactocerebrosidase in leukocytes (CBGC / Galactocerebrosidase, Leukocytes) or fibroblasts (CBGT / Galactocerebrosidase, Fibroblasts) along with psychosine analysis can indicate a diagnosis of Krabbe disease. Molecular sequencing of the GALC gene (GALCS / Krabbe Disease, Full Gene Analysis and Large [30 kb] Deletion, PCR) allows for detection of the disease-causing mutations in affected patients and carrier detection in family members.

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

Quantification of psychosine (galactosylsphingosine) in dried blood spots supports the biochemical diagnosis and follow-up of individuals affected with Krabbe disease

Interpretation Provides information to assist in interpretation of the test results

An elevation of psychosine is indicative of Krabbe disease.

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

This test is not capable of identifying Krabbe carriers.

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.

Normal <10 nmol/L psychosine

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

1. Orsini J, Morrissey M, Slavin L, et al: Implementation of newborn screening for Krabbe disease: Population study and cutoff determination. Clin Biochem 2009;42:877-884

2. Svennerholm L, Vanier M, Mansson J: Krabbe disease: a galactosylsphingosine (psychosine) lipidosis. J Lipid Res 1980;21:53-64

3. Enns GM, Steiner RD, Cowan TM: Lysosomal Disorders. In Pediatric Endocrinology and Inborn Errors of Metabolism. Edited by Sarafoglou K, Hoffman G, Roth KS. New York, McGraw-Hill Medical, 2009, p 744


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