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Confirming a diagnosis of Niemann-Pick type C disease

Laboratory testing for Niemann-Pick type C disease (NP-C) is complex and sometimes difficult to interpret as shown in Figure 1. A combination of biochemical testing, histological analysis and genetic testing are used to confirm the diagnosis of NP-C. Magnetic resonance imaging (MRI) can also be used to detect cerebral atrophy or changes in white matter.1

Figure 1: The algorithm for laboratory diagnosis of NP-C (Patterson et al, 2012) 1

 

Biochemical testing


Filipin staining of fibroblasts is a key diagnostic test for NP-C. Fibroblasts cultured from skin biopsy are filipin stained and observed for 3 to 4 weeks using fluorescence microscopy for evidence of the impaired intracellular cholesterol transport and cholesterol storage patterns typically seen in 80-85% of NP-C cases.1

Filipin tests require analysis in specialized diagnostic centers, which takes around 6 to 8 weeks. Results may be difficult to interpret, particularly in adults with varying biochemical phenotypes. However, results of filipin tests are accurate, with very few false negatives and almost no false positives.


Control subject
No marking

NP-C subject
Fluorescent vacuoles in lysosomes marked
with the accumulation of cholesterol
 

How to perform a skin biopsy

This video shows how to perform a skin biopsy, which is required in order to carry out a filipin test. This film has been developed with expert help from Dr Frédéric Sedel, MD, PhD, coordinator of a Neurometabolic Unit at Pitié-Salpêtrière Hospital, Paris and of a Neurometabolic research group at University Pierre & Marie Curie, Paris.

Step-by-step guide to carrying out a skin biopsy:

  • Give anaesthesia (EMLA cream for one hour)
  • Disinfect with alcohol or benzalconium chloride (avoid iodine antiseptics because it prevents the growth of fibroblasts)
  • Sample a piece of skin (1 cm length, 1-2 mm thick) by using a sterile curved clamp and a sterile scalpel as shown in the video
  • Put the skin into a sterile saline solution (NaCl 0.9 %)
  • Clean the skin with a sterile solution (iodine is allowed)
  • Apply sterile strips to keep the wound together
  • Apply a bandage with a waterproof film and leave for seven days without changing it

 

Genetic testing


DNA sequencing is ideally performed in parallel with filipin staining (the primary diagnostic methodology) to confirm NP-C diagnosis and determine the presence of identifiable pathological NP-C gene mutations present in 99% of cases. In newly-diagnosed patients it can also be used to identify affected siblings, detect carriers in blood relatives and identify NPC2 patients who may benefit from hematopoietic stem cell transplantation. Parental DNA testing can also confirm allele segregation and homozygous status.1

 

Plasma oxysterol testing


Plasma oxysterol testing is a relatively new biochemical test. Early data show that levels of these cholesterol oxidation products as NP-C biomarkers may form ancillary test to aid diagnosis of patients with unclear biochemical phenotypes and NP-C gene mutations.1

 

Bone marrow biopsy


Aspiration and examination of bone marrow may show foam cells and provide a measure of disease burden in late disease. It can provide a rapid screening test in cases where bone marrow is readily available.1

 

Electron microscopy


Electron microscopy of skin or liver biopsy can show polymorphous cytoplasmic bodies.

 

Imaging


MRI can be used to detect white matter changes in early-infantile onset NP-C and cerebral and/or cerebellar atrophy in patients with late-onset neurological disease. Other imaging techniques, such as proton magnetic resonance spectroscopic imaging (H-MRSI), diffusion tensor imaging (DTI) and magnetic transfer ratio (MTR) imaging are all approaches that may have potential use in quantifying brain changes that may prove useful in the future.1

 

References

  1. Patterson MC, Hendriksz CJ, Walterfang M, et al, on behalf of the NP-C Guidelines Working Group. Recommendations for the diagnosis and management of Niemann–Pick disease type C: An update. Mol Genet Metab 2012. 106(3):330-344.