Test ID: GALCK
Krabbe Disease, Known Mutation

Carrier testing of individuals with a family history of Krabbe disease when a mutation(s) has been identified in an affected family member

Diagnostic confirmation of Krabbe disease when familial mutations have been previously identified

Documentation of the specific familial mutation(s) must be provided with the specimen in order to perform this test.

If skin biopsy is received, fibroblast culture for genetic test will be added and charged separately.

For prenatal specimens only: If amniotic fluid (non-confluent cultured cells) is received, amniotic fluid culture/genetic test will be added and charged separately. If chorionic villus specimen (non-confluent cultured cells) is received, fibroblast culture for genetic test will be added and charged separately. For any prenatal specimen that is received, maternal cell contamination studies will be added.

• Molecular Genetics-Biochemical Disorders Patient Information Sheet
• Informed Consent for Genetic Testing

Polymerase Chain Reaction (PCR) Followed by DNA Sequencing Analysis and/or Follow up PCR is utilized to test for the presence of mutations previously identified in an affected family member.

(PCR is utilized pursuant to a license agreement with Roche Molecular Systems, Inc.)      

Forms:

1. Molecular Genetics-Biochemical Disorders Patient Information Sheet (Supply T527) in Special Instructions

2. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.

Specimen must arrive within 96 hours of collection.

Submit only 1 of the following specimens:

Preferred:

Specimen Type: Whole blood

Container/Tube:

Preferred: Lavender top (EDTA) or yellow top (ACD)

Acceptable: Any anticoagulant

Specimen Volume: 3 mL      

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.

Specimen Stability Information: Ambient (preferred)/Refrigerated

Specimen Type: Cultured fibroblasts

Container/Tube: T-75 or T-25 flask

Specimen Volume: 1 full T-75 or 2 full T-25 flasks

Specimen Stability Information: Ambient (preferred)/Refrigerated <24 hours

Due to the complexity of prenatal testing, consultation with the laboratory is required for all prenatal testing. Prenatal specimens can be sent Monday through Thursday and must be received by 5 p.m. CST on Friday in order to be processed appropriately. All prenatal specimens must be accompanied by a maternal blood specimen. Order MCC/88636 Maternal Cell Contamination, Molecular Analysis on the maternal specimen.

Specimen Type: Amniotic fluid

Container/Tube: Amniotic fluid container

Specimen Volume: 20 mL

Specimen Stability Information: Refrigerated (preferred)/Ambient

Specimen Type: Chorionic villi

Container/Tube: 15-mL tube containing 15 mL of transport media

Specimen Volume: 20 mg

Specimen Stability Information: Refrigerated

Acceptable:

Specimen Type: Confluent cultured cells

Container/Tube: T-25 flask

Specimen Volume: 2 flasks

Collection Instructions: Submit confluent cultured cells from another laboratory.

Specimen Stability Information: Ambient (preferred)/Refrigerated

Specimen Type: Skin biopsy

Container/Tube: Sterile container with any standard cell culture media (eg, minimal essential media, RPMI 1640). The solution should be supplemented with 1% penicillin and streptomycin. Tubes can be supplied upon request (Eagle's minimum essential medium with 1% penicillin and streptomycin [Supply T115]).

Specimen Volume: 4-mm punch

Specimen Stability Information: Refrigerated (preferred)/Ambient

Acceptable:

Specimen Type: Blood spot

Container/Tube: Whatman Protein Saver 903 Paper

Specimen Volume: 5 blood spots

Collection Instructions:

1. Let blood dry on the filter paper at ambient temperature in a horizontal position for 3 hours.

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

3. Do not stack wet specimens.

4. Keep specimen dry.

Specimen Stability Information: Ambient (preferred)/Refrigerated

Krabbe disease (globoid cell leukodystrophy) is an autosomal recessive disorder caused by a deficiency of galactocerebrosidase (GALC, galactosylceramide beta-galactosidase). GALC is encoded by the GALC gene located on 14q31. Krabbe disease occurs in approximately 1 in 100,000 live births with a carrier frequency of about 1 in 150 in the general population. Deficiency of GALC activity leads to an accumulation of galactosylceramide in globoid cells (multinucleated macrophages) causing severe demyelination throughout the brain. The toxic metabolite galactosylsphingosine (psychosine), an apoptotic compound, accumulates in oligodendrocytes and Schwann cells and contributes to disease pathogenicity.

Severely affected individuals typically present between 3 to 6 months of age with increasing irritability and sensitivity to stimuli. Rapid neurodegeneration follows with death usually occurring by age 13 months. There are later onset forms of the disease that are characterized by ataxia, vision loss, weakness, and psychomotor regression. 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.

The recommended first-tier test for Krabbe disease is LDSBS/89406 Lysosomal Disorders Screen, Blood Spot, CBGC/8816 Galactosylceramide Beta-Galactosidase, Leukocytes, or CBGT/8297 Galactosylceramide Beta-Galactosidase, Fibroblasts. Individuals with GALC activity below the reference range for these assays are more likely to have mutations in the GALC gene that are identifiable by molecular genetic testing. The above tests are not reliable for detection of carriers of Krabbe disease. Molecular genetic testing (this test) is the recommended test for individuals with a family history of Krabbe disease in which the mutations in the family are known. The recommended molecular test if mutations in the family are not known is GALCS/60696 Krabbe Disease, Full Gene Analysis and Large (30 kb) Deletion, PCR.

This assay tests for specific mutations previously identified in a family member and, therefore, may also be used for diagnosing individuals with a suspected diagnosis of Krabbe disease when mutations in the family are known. While enzyme activity is not predictive of age of onset, there are known genotype-phenotype correlations. The common 30-kb deletion spanning intron 10 through the end of the gene accounts for a significant proportion of disease alleles that contribute to infantile Krabbe disease. Individuals who are homozygous for the deletion, or compound heterozygous for the deletion and a second GALC mutation (with the exception of late-onset mutations), are predicted to have infantile Krabbe disease. The c.857G->A (p.Gly286Asp) mutation, on the other hand, is only associated with a late-onset phenotype.

An interpretive report will be provided.

An interpretive report will be provided.

The identification of a disease-causing mutation in an affected family member is necessary before testing can be offered for other family members. If a familial mutation has not been previously identified, order GALCS/60696 Krabbe Disease, Full Gene Analysis and Large (30 kb) Deletion, PCR.

Analysis is performed for the familial mutations provided only. This assay does not rule-out the presence of other mutations within this gene or within other genes that may be associated with metabolic disease.

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete.

A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories for instructions for testing patients who have received a bone marrow transplant.

1. Wenger DA: Krabbe Disease (Most recent review March 2011). Available at http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=krabbe

2. Luzi P, Rafi MA, Wenger DA: Structure and organization of the human galactocerebrosidase (GALC) gene. Genomics 1995;26:407-409

3. Luzi P, Rafi MA, Wenger DA: Characterization of the large deletion in the GALC gene found in patients with Krabbe disease. Hum Mol Genet 1995;4(12):2335-2338

4. Spiegel R, Bach G, Sury V, et al: A mutation in the saposin A coding region of the prosaposin gene in an infant presenting as Krabbe disease: report of saposin A deficiency in humans. Molec Genet Metab 2005,84:160-166

DNA sequencing is utilized to test for the presence of a specific mutation(s) in the GALC gene that was previously identified in an affected family member(Unpublished Mayo method)

Thursday; 10 am

Krabbe Disease, Known Mutation

81479 - Unlisted molecular pathology procedure 

Amniotic Fluid Culture for Genetic Testing

88235-Tissue culture for amniotic fluid (if appropriate)

88240-Cryopreservation (if appropriate)

Fibroblast Culture for Genetic Testing

88233-Tissue culture, skin or solid tissue biopsy (if appropriate)

88240-Cryopreservation (if appropriate)

Maternal Cell Contamination, Molecular Analysis

81265- Comparative analysis using Short Tandem Repeat (STR) markers; patient and comparative specimen (eg, pre-transplant recipient and donor germline testing, post-transplant non-hematopoietic recipient germline [eg, buccal swab or other germline tissue sample] and donor testing, twin zygosity testing or maternal cell contamination of fetal cells