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Laboratory Test Directory

GALC Gene Deletion/Duplication, Krabbe Disease

Components

Name Method Department Units
GALC Gene Deletion/Duplication, Krabbe Disease Multiplex ligation-dependent probe amplification (MLPA)
DNA extraction
Molecular Genetics

Specimen Requirements

Whole blood

Container Type Container Size Specimen Volume
Preferred

Purple tube (EDTA)

4 mL 2 mL-4 mL
Stability

Room temperature - 24 hour(s)
Refrigerated - 72 hour(s)

Alternate

Purple tube (EDTA)

Micro sample tube 2 mL-4 mL
Stability

Room temperature - 24 hour(s)
Refrigerated - 72 hour(s)

Specimen Preparation

  • Do not freeze
  • Do not centrifuge

Reasons for Rejection

  • Clotted specimen
  • Centrifuged specimen
  • Frozen specimen
  • Wrong collection tube

Comments

One EDTA blood tube containing a minimum 1mL whole blood can be used to perform all molecular genetic tests for Krabbe disease; no need to draw additional EDTA tube for each molecular genetic test. For infants under 4 weeks of age, blood sample from heel- or finger-stick collected in EDTA micro sample tube / microtainer is accepted (a minimum 1mL required).

Please click on the Lab Form Link in the Forms Section to print and complete the Genetic Test Requisition Form. Submission of completed Genetic Test Requisition Form is required, and submission of informed consent form is recommended. Please send clinical information with Requisition Form.

Krabbe disease is an autosomal recessive lysosomal storage disorder resulting from deficiency of the galactocerebrosidase enzyme encoded by the GALC gene. In almost all patients, deficient galactocerebrosidase enzyme activity (0-5% of normal activity) is seen. About 85-90% of patients with Krabbe disease have infantile-onset form, while the remaining 10-15% of patients has later-onset form of the disease. Infantile-onset (classic) form is characterized by presentation within the first 6 months of life with extreme irritability, spasticity, and developmental delay, and it causes progressive motor and neurologic deterioration and death before age two years. Later onset (late-infantile, juvenile, or adult-onset) forms have less severe disease severity and slower progression. The most common pathogenic variant in the GALC gene seen in patients with Krabbe disease is the 30-kb deletion involving exons 11 through 17, which accounts for about 45% of the pathogenic alleles in European ancestry population and about 35% of the pathogenic alleles in Mexican ancestry population. The majority of remaining pathogenic alleles in the GALC gene are smaller sequence variants detectable by GALC gene sequencing. Rare deletion/duplication in the GALC gene that cannot be detected by the GALC 30-kb deletion detection test or the GALC gene sequencing have been reported in several patients with Krabbe disease, and pathogenic sequencing variant in both alleles of the PSAP gene has also been reported in a rare case of Krabbe disease. This test is a comprehensive deletion/duplication analysis of the GALC gene done by multiplex ligation-dependent probe amplifcation (MLPA) method. This test will be performed as a STAT testing, with expected result turnaround time of 7 days or less. For evaluation of newborns with positive newborn screening for Krabbe disease, it is recommended to first order the GALC common 30-kb deletion detection by PCR (test code KDGALCCD) and GALC gene sequencing (test code KDGALCSEQ) prior to ordering this test. This test is typically performed as a reflex test when results are negative or only one pathogenic variant is detected by GALC 30-kb deletion detection test and GALC gene sequencing. If this test result is normal but patient is still suspected to have Krabbe disease, then reflex to PSAP gene sequencing (test code KDPSAPSEQ) can be requested - please contact the laboratory or indicate this on the lab order if reflex to PSAP gene sequencing is desired.

For family members with a proband with a known GALC gene deletion or duplication (that is not the common 30-kb deletion), this testing can be performed as a carrier testing.

CPT Code

  • 81479