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Test Catalog

Test ID: PSYCF    
Psychosine, Spinal Fluid

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

Aids in the biochemical diagnosis of Krabbe disease using cerebrospinal fluid specimens

 

Follow-up of individuals affected with Krabbe disease

 

Follow-up testing after an abnormal newborn screening result for Krabbe disease

 

Monitoring of individuals at risk to develop late onset Krabbe disease

 

Monitoring of individuals with Krabbe disease after hematopoietic stem cell transplantation

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

This test is used as a biomarker of Krabbe disease for individuals with reduced galactocerebrosidase (GALC) activity and for monitoring of patients with Krabbe disease and Saposin A cofactor deficiency. In cerebrospinal fluid (CSF), psychosine is typically ordered when CSF is collected primarily to determine protein content in a patient at risk of or monitored for the development of signs of Krabbe disease.

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 disorder caused by deficient activity of the enzyme galactocerebrosidase (GALC). GALC facilitates the lysosomal degradation of psychosine (galactosylsphingosine) and 3 other substrates (galactosylceramide, lactosylceramide, and lactosylsphingosine). Krabbe disease is caused by mutations in the GALC gene, and it has an estimated frequency of 1 in 250,000 births.

Eighty-five percent to 90% of patients present before the first year of life with central nervous system impairment including increasing irritability, developmental delay, and sensitivity to stimuli. Rapid neurodegeneration including white matter disease follows, with death usually occurring by 2 years of age. Ten percent to 15% of individuals have later onset variants of the disease that are characterized by ataxia, vision loss, weakness, and psychomotor regression, presenting anytime from 6 months to the seventh decade of life. The clinical course of Krabbe disease can be variable, even within the same family.

 

Newborn screening for Krabbe disease has been implemented in some states. The early (presymptomatic) identification and subsequent testing of infants at risk for Krabbe disease may be helpful in reducing the morbidity and mortality associated with this disease. While treatment is mostly supportive, hematopoietic stem cell transplantation has shown some success if performed prior to onset of neurologic damage.

 

Psychosine (PSY) is a neurotoxin at elevated concentrations. Importantly, it is 1 of 4 substrates degraded by GALC. It has been shown to be elevated in patients with active Krabbe disease or with Saposin A cofactor deficiency, and therefore, may be a useful biomarker for the presence of disease or disease progression.

Reduced or absent GALC in leukocytes (CBGC / Galactocerebrosidase, Leukocytes) or dried blood spots (PLSD / Lysosomal and Peroxisomal Storage Disorders Screen, Blood Spot) along with psychosine analysis can indicate a diagnosis of Krabbe disease. Molecular sequencing of the GALC gene (KRABZ / 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.

 

Individuals with a disease phenotype similar to Krabbe disease may have Saposin A cofactor deficiency. Saposin A cofactor deficiency also results in elevated psychosine levels. Testing for this condition via molecular analysis of PSAP is useful in those with elevated psychosine and normal to reduced GALC activity with normal molecular genetic GALC analysis.

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 < 0.04 nmol/L

Interpretation Provides information to assist in interpretation of the test results

An elevation of psychosine is indicative of Krabbe disease or Saposin A cofactor deficiency.

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

Asymptomatic patients with later onset Krabbe disease may have a normal psychosine concentration in cerebrospinal fluid (CSF).

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Kwon JM, Matern D, Kurtzberg J, et al: Consensus guidelines for newborn screening, diagnosis and treatment of infantile Krabbe disease. Orphanet J Rare Dis. 2018;13(1):30 doi: 10.1186/s13023-018-0766-x

2. Orsini JJ, Escolar ML, Wasserstein MP, et al: Krabbe Disease. In GeneReviews Edited by: MP Adam, HH Ardinger, RA Pagon: University of Washington, Seattle. 1993-2019. 2000 Jun 19 [Updated 2018 Oct 11]. Accessed May 2019. Available at: www.ncbi.nlm.nih.gov/books/NBK1238/

3. Turgeon CT, Orsini JJ, Sanders KA, et al: Measurement of psychosine in dried blood spots - a possible improvement to newborn screening programs for Krabbe disease. J Inherit Metab Dis. 2015;38: 923–929

4. Wenger DA, Escolar ML, Luzi P, Rafi MA: Krabbe disease (Globoid Cell Leukodystrophy). In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL BeaudetL, B Vogelstein, KW Kinzler, SE Antonarakis, A Ballabio, K Gibson, G Mitchell. New York, NY: McGraw-Hill; 2014 Accessed March 20, 2019. Available at: http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62644214