Diagnosis of Niemann-Pick Disease Type C Using a Glycinated Bile Acid Biomarker (N-(3β,5α,6β-Trihydroxy-cholan-24-oyl)glycine)
Washington University Metabolomics Facility is a Clinical Laboratory Improvement Amendment (CLIA) certificated laboratory. We are pleased to offer free diagnostic test for Niemann-Pick disease type C (NPC) using N-(3β,5α,6β-trihydroxy-cholan-24-oyl)glycine that is a NPC-specific bile acid biomarker.
1. Clinical Significance and Principle
Niemann-Pick disease type C (NPC) is a fatal, neurodegenerative, cholesterol storage disorder. Mutations in the NPC1 and NPC2 genes are responsible for NPC in humans, with 95% of cases associated with mutations in NPC1. The heterogeneous NPC symptoms comprise neonatal cholestatic jaundice, hepatosplenomegaly, vertical supranuclear gaze palsy, gelastic cataplexy, ataxia, dysphagia, dystonia, cognitive impairment and psychosis. The current diagnostic standard for NPC includes clinical assessment, biomarker testing, and genetic analysis. All patients with suspicion of NPC and patient groups with an increased risk of NPC are recommended to receive biomarker profiling or genetic test that are first-line diagnostic tests for NPC. The most well validated NPC diagnostic biomarkers include cholestane-3b,5a,6b-triol (C-triol), lysoSM-509 (N-palmitoyl-O-phosphocholineserine), and the glycinated bile acid (N-(3β,5α,6β-trihydroxy-cholan-24-oyl)glycine). All are significantly elevated in NPC plasma. Although these three biomarkers are equally sensitive in detection of NPC patients, the glycinated bile acid is the most specific. The diagnosis of patients with high clinical suspicion and/or a biomarker profile should be confirmed with genetic test.
2. Specimen Collection, Handling and Storage
It is recommended that the specimen donors fast 12 hours prior to specimen collection, though this is not required.
Whole blood should be spun at 2200 rpm for 10 minutes within 18 hour at room temperature or 4 oC after being drawn from subject, and plasma transferred to a new polypropylene tube. Ethylenediamine tetraacetic acid dipotassium salt (EDTA-K2) or lithium heparin as anti-coagulant is acceptable. The hemolyzed plasma with hemoglobin up to 800mg/dL is also acceptable. Optimum sample volume is 0.2 mL; minimum volume is 0.07 mL. The glycinated bile acid is stable in plasma at room temperature or 37 oC for at least 5 days, at -80 oC for at least 448 days, and after 5 freeze/thaw cycles.
3. Sample submission
Please download and fill out the NPC diagnostic test request form. Plasma samples from outside sources can be shipped at room temperature within 5 days, though shipment with dry ice is preferred. The shipping address is:
Attn: David Scherrer
BJC Institute of Health
10th floor, Room 10402
425 South Euclid Avenue
St. Louis, MO 63110
The test report will be sent to the contact person who requests the analyses. The range of the glycinated bile acid in control, heterozygote, and NPC1 subjects are <1 – 16.8 ng/mL, <1 – 43.3 ng/, and 10.1 – 897 ng/mL, respectively. Receiver-operator curve (ROC) analysis demonstrated that the area under the curve for glycinated bile acid is 0.9999. The assay with cutoff value of 18.5 ng/mL has sensitivity of 0.9945 and specificity of 0.9982. Any patient samples with glycinated bile acid levels >18.5 ng/mL are considered to require follow-up with genetic analysis.
The glycinated bile acid in acid-sphingomyelinase deficiency (ASMD), lysosomal acid lipase deficiency (LALD), including cholesteryl ester storage disease and Wolman disease, is above the cutoff (18.5 ng/mL) for NPC disease and overlaps with that in NPC. Sphingomyelinase and lysosomal lipase assays as well as genetic test are required to further differentiate NPC from ASMD and LALD.