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Test ID: PSY Psychosine, Blood Spot

Useful For

Aids in the biochemical diagnosis of Krabbe disease and saposin A cofactor deficiency

 

Follow-up of individuals affected with Krabbe disease

 

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

 

This test is not capable of identifying carriers of Krabbe disease.

Reporting Name

Psychosine, BS

Specimen Type

Whole blood


Advisory Information


This test is recommended for newborns or infants who have not had previous psychosine testing.

 

If requesting psychosine testing for either diagnostic or monitoring purposes, order PSYR / Psychosine, Whole Blood.



Shipping Instructions


 



Specimen Required


Supplies: Card-Blood Spot Collection (Filter Paper) (T493)

Container/Tube:

Preferred: Card-Blood Spot Collection (Filter Paper)

Acceptable: Ahlstrom 226 filter paper, Munktell filter paper, Whatman protein Saver 903 paper, or blood collected in tubes containing heparin or EDTA and dried on filter paper

Specimen Volume: 2 blood spots

Collection Instructions:

1. Completely fill at least 2 circles on the filter paper card (approximately 100 microliters blood per circle).

2. Let blood dry on filter paper at ambient temperature in a horizontal position for 3 or more hours.

3. Do not expose specimen to heat or direct sunlight.

4. Do not stack wet specimens.

5. Keep specimen dry.

Additional Information:

1. For collection instructions, see Blood Spot Collection Instructions in Special Instructions.

2. For collection instructions in Spanish, see Blood Spot Collection Card-Spanish Instructions (T777) in Special Instructions.

3. For collection instructions in Chinese, see Blood Spot Collection Card-Chinese Instructions (T800) in Special Instructions.


Specimen Minimum Volume

1 blood spot

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole blood Ambient (preferred) 96 days FILTER PAPER
  Frozen  96 days FILTER PAPER
  Refrigerated  96 days FILTER PAPER

Clinical Information

Krabbe disease (globoid cell leukodystrophy) is an autosomal recessive lysosomal storage disorder caused by an enzyme deficiency of galactocerebrosidase (GALC). GALC facilitates the lysosomal degradation of psychosine (galactosylsphingosine) and 3 other substrates (galactosylceramide, lactosylceramide and lactosylsphingosine). Krabbe disease is caused by variants in the GALC gene, and it has an estimated frequency of 1 in 100,000 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 age 2. Ten percent to 15% of individuals have late onset forms of the disease that are characterized by ataxia, vision loss, weakness, and psychomotor regression presenting anytime from age 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 early, usually within the first 2 months of life.

 

Psychosine is 1 of 4 substrates degraded by GALC and is a neurotoxin at elevated concentrations. Psychosine has been shown to be elevated in patients with symptomatic 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, Varies) allows for detection of the disease-causing variants 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 the PSAP gene is useful in those with elevated psychosine and normal to reduced GALC activity with normal GALC sequencing.

Reference Values

Normal <2 nmol/L psychosine

Interpretation

An interpretive report will be provided.

 

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

Clinical Reference

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: Sarafoglou K, Hoffman G, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. McGraw-Hill Medical; 2009:744

4. 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 Sep;38(5):923-929

5. Wenger DA, Escolar ML, Luzi P, Rafi MA:  Krabbe disease (Globoid Cell Leukodystrophy). In: Valle D, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019. Accessed March 20, 2019. Available at https://ommbid.mhmedical.com/content.aspx?sectionid=225546481&bookid=2709&Resultclick=2

Day(s) and Time(s) Performed

Monday through Sunday; 7 a.m.

Analytic Time

2 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
PSY Psychosine, BS 93688-0

 

Result ID Test Result Name Result LOINC Value
62235 Psychosine 93688-0
36342 Reviewed By 18771-6
36343 Interpretation (PSY) 59462-2

Method Name

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

Forms

1. Biochemical Genetics Patient Information (T602) in Special Instructions.

2. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

mml-biochemical