Diagnostic tests for Niemann-Pick disease type C (NP-C): A critical review

Abstract

Niemann-Pick disease type C (NP-C) is a neurovisceral lysosomal cholesterol trafficking and lipid storage disorder caused by mutations in one of the two genes, NPC1 or NPC2. Diagnosis has often been a difficult task, due to the wide range in age of onset of NP-C and clinical presentation of the disease, combined with the complexity of the cell biology (filipin) laboratory testing, even in combination with genetic testing. This has led to substantial delays in diagnosis, largely depending on the access to specialist centres and the level of knowledge about NP-C of the physician in the area. In recent years, advances in mass spectrometry has allowed identification of several sensitive plasma biomarkers elevated in NP-C (e.g. cholestane-3β,5α,6β-triol, lysosphingomyelin isoforms and bile acid metabolites), which, together with the concomitant progress in molecular genetic technology, have greatly impacted the strategy of laboratory testing. Specificity of the biomarkers is currently under investigation and other pathologies are being found to also result in elevations. Molecular genetic testing also has its limitations, notably with unidentified mutations and the classification of new variants. This review is intended to increase awareness on the currently available approaches to laboratory diagnosis of NP-C, to provide an up to date, comprehensive and critical evaluation of the various techniques (cell biology, biochemical biomarkers and molecular genetics), and to briefly discuss ongoing/future developments. The use of current tests in proper combination enables a rapid and correct diagnosis in a large majority of cases. However, even with recent progress, definitive diagnosis remains challenging in some patients, for whom combined genetic/biochemical/cytochemical markers do not provide a clear answer. Expertise and reference laboratories thus remain essential, and further work is still required to fulfill unmet needs.

The Spectrum of Niemann-Pick Type C Disease in Greece

“…Very low rates are described in patients with the "classical" filipin staining pattern with the "variant" phenotype showing a moderate or nonsignificant impairment. Although the test was till recently used as a secondary diagnostic test, the above observation along with the complexity and the cost of the test have practically limited its use to research settings (Vanier et al 2016). The rate of LDL induced cholesteryl ester formation, studied in nine of our patients (Table 2) was diagnostic for all, although with variations, in accordance with previous reports.…”

“…A critical review of the currently available diagnostic approaches has recently been published (Vanier et al 2016).…”

“…The filipin test was developed about 30 years ago and, till recently, it was considered the gold standard method for diagnosing NPC (Vanier et al 2016). It is used in fibroblasts loaded with LDL to demonstrate the impaired intracellular transport of endocytosed cholesterol through the fluorescent staining of non-esterified cholesterol accumulated in the late endosome/lysosome compartment (Vanier and Latour 2015).…”

“…The majority of cases (80-85%) show a "classical" staining pattern characterized by the presence of numerous strongly fluorescent perinuclear vesicles that are cholesterol loaded. In the remaining cases a less intense and variable, "variant," staining pattern, that can be a source of confusion, is observed (Vanier et al 2016). In our cohort of patients the filipin test was performed in 14/14 patients.…”

SERAC1 deficiency causes complicated HSP: evidence from a novel splice mutation in a large family

“…The two family members of family branch II presenting with a more multisystemic juvenile-onset cHSP indicate an intermediate phenotype between the oligosystemic cHSP and the classic infantile cluster along this gradual spectrum of SERAC1 deficiency. Other diseases with a similar gradual phenotypic spectrum ranging from frequent, multisystemic infantile-onset phenotypes to more rare, oligosystemic juvenile-onset phenotypes are lysosomal storage diseases and in particular Niemann-Pick type C, which can be conceptualised similarly to SERAC1 20. cHSP, complicated hereditary spastic paraplegia; MEGDEL, 3-methylglutaconic aciduria, deafness, encephalopathy, Leigh-like syndrome.…”