What is the sensitivity and specificity of beta-galactocerebrosidase (GALC) enzyme?

From the Guidelines

Betagalactocerebrosidase enzyme testing has high sensitivity and specificity for diagnosing Krabbe disease, typically exceeding 95% for both measures when performed in specialized laboratories. This lysosomal enzyme assay measures the activity of galactocerebrosidase (GALC), with significantly reduced activity indicating Krabbe disease 1. The test can be performed on various specimens including leukocytes, fibroblasts, or dried blood spots, with leukocytes generally providing the most reliable results.

Key Considerations

• False negatives can occur in patients with certain GALC gene mutations that produce enzymatically active but clinically ineffective enzyme, while false positives may be seen in heterozygous carriers who have intermediate enzyme levels.
• For optimal diagnostic accuracy, enzyme testing should be combined with GALC gene sequencing, particularly when clinical suspicion is high despite borderline enzyme results 1.
• Psychosine (galactosylsphingosine) measurement serves as a valuable biomarker that can improve diagnostic specificity, as it accumulates specifically in Krabbe disease.
• The interpretation of results requires consideration of age-specific reference ranges, as enzyme activity naturally varies throughout development.

Diagnostic Approach

• Enzyme testing should be interpreted in the context of clinical history and other pertinent tests, such as biomarker testing and DNA sequencing 1.
• Molecular testing can help confirm enzymatic diagnosis, identify pathogenic variants, and provide insight into management and prognosis 1.
• Carrier screening for Krabbe disease is not reliable using enzymatic testing alone and should be performed using molecular studies.

From the Research

Betagalactocerebrosidase Enzyme Sensitivity and Specificity

• The sensitivity and specificity of betagalactocerebrosidase enzyme assays have been evaluated in several studies 2, 3, 4.
• A study published in 2009 developed a novel assay for measuring beta-galactocerebrosidase activity, which showed high specificity and could detect activity in as little as 2 microg of cell protein extract or 7.5 microg of tissue 2.
• Another study published in 2016 reported on the newborn screening for Krabbe disease in New York State, which used a mass spectrometry-based assay to measure GALC enzyme activity, and found that the positive predictive value of KD screening was 1.4% 3.
• A 2021 study developed and clinically validated a leukocyte enzymatic assay using liquid chromatography tandem mass spectrometry (LC-MS/MS) to measure GALC activity, which showed good sensitivity and specificity for diagnosing Krabbe disease 4.
• The specificity of betagalactocerebrosidase enzyme assays is crucial for diagnosing Krabbe disease, as false positives can lead to unnecessary treatment and false negatives can delay diagnosis and treatment 2, 3, 4.

Factors Affecting Enzyme Activity

• The activity of betagalactocerebrosidase enzyme can be affected by various factors, including pH, salt concentration, and surfactants 5.
• A study published in 2019 found that the self-association of human beta-galactocerebrosidase is dependent on pH, salt concentration, and surfactants, and that the enzyme has a tendency for reversible self-association 5.
• Understanding the factors that affect enzyme activity is important for developing accurate and reliable assays for diagnosing Krabbe disease 5.

Clinical Applications

• Betagalactocerebrosidase enzyme assays have important clinical applications, including diagnosing Krabbe disease and monitoring the efficacy of treatment 2, 3, 4, 6.
• A study published in 2016 reviewed the insights into the pathogenesis and treatment of Krabbe disease, and highlighted the importance of early diagnosis and treatment for improving outcomes 6.
• The development of sensitive and specific assays for measuring betagalactocerebrosidase activity is crucial for improving the diagnosis and treatment of Krabbe disease 2, 3, 4, 6.