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Test ID: PSYR Psychosine, Whole Blood


Shipping Instructions


Must be sent refrigerated.



Necessary Information


1. Patient’s age is required.

2. Date of hematopoietic stem cell transplantation (HSCT), if performed.



Specimen Required


Collection Container/Tube:

Preferred: Lavender top (EDTA)

Acceptable: Green top (sodium heparin, lithium heparin)or yellow top (ACD)

Specimen Volume: 2 mL


Useful For

Aiding in the biochemical diagnosis of Krabbe disease using whole blood 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

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

Psychosine, RBC

Specimen Type

Whole blood

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole blood Refrigerated 7 days

Clinical Information

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 alterations 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 (GALCW / 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, Varies) allows for detection of the disease-causing alterations 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 moderately reduced GALC activity with normal molecular genetic GALC analysis.

Reference Values

Normal <10 pmol/g Hb

Interpretation

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

Clinical Reference

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 Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet].  University of Washington, Seattle; 2000.  Updated October 11, 2018.. 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: Valle D, Beaudet AL, Vogelstein LB, et al, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2014 Accessed March 20, 2019. Available at: http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62644214

Day(s) Performed

Tuesday, Thursday

Report Available

3 to 7 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

82542

LOINC Code Information

Test ID Test Order Name Order LOINC Value
PSYR Psychosine, RBC 93687-2

 

Result ID Test Result Name Result LOINC Value
606152 Interpretation (PSYR) 59462-2
606145 Psychosine, RBC 93687-2
606151 Reviewed By 18771-6
Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

mml-biochemical