Genetic and laboratory diagnostic approach in Niemann Pick disease type C

Abstract

Niemann Pick disease type C (NP-C) is a rare autosomal recessive disorder that results from mutations in either the NPC1 or the NPC2 gene. The estimated incidence of NP-C is 1 in 120,000 live births, although the frequency of cases is higher in some isolated populations. More than 350 different NPC1 and NPC2 gene mutations have been reported in patients with confirmed diagnoses. Approximately 95 % of patients harbour mutations in NPC1, with most of the remaining patients having NPC2 mutations. The traditional methods for diagnosing patients with NP-C include histopathological analysis of bone marrow aspirate, liver and skin biopsies, fluorescent and electron microscopy, and cholesterol esterification assays. New laboratory methods that use mass spectroscopy for detection of cholesterol metabolism products are promising to become part of the routine diagnostic and screening tests in the near future, but further evaluation is required to determine the sensitivity and specificity of these analyses in patients with different age-at-onset forms of NP-C. Although filipin staining and cholesterol esterification studies performed in patient skin fibroblasts can, in experienced hands, provide a robust approach to diagnosing NP-C, they are only available in a few specialist laboratories. Thus, sequencing of NPC1 and NPC2 is currently the most universally accessible diagnostic technique in this disorder.

Selective screening of Niemann–Pick type C Brazilian patients by cholestane-3β,5α,6β-triol and chitotriosidase measurements followed by filipin staining and NPC1/NPC2 gene analysis

“…Therefore, clinical presentation is mainly characterized by neurological dysfunction and liver damage [4,5]. The neurological symptoms, including vertical supranuclearophthalmoplegia, cataplexy, dysarthria, dysphagia, seizures, speaking and swallowing difficulty and dementia, may differ greatly between patients in terms of age-at-onset, clinical presentation, disease severity and course of the neurodegeneration, making difficult the prompt recognition of this pathology [6][7][8].…”

“…The demonstration of impaired intracellular cholesterol transport and homeostasis is considered the most specific functional diagnostic test for NPC [8]. This test uses skin fibroblasts cultured in LDL-enriched medium and is able to detect unesterified cholesterol upon staining with filipin-a fluorescent chemical compound [11].…”

Diagnostic workup and management of patients with suspected Niemann-Pick type C disease

“…Chitotriosidase is mildly elevated in many cases of NP-C but normal values are also possible [McKay Bounford and Gissen, 2014], whereas in other lysosomal storage disorders, such as Gaucher disease (GD) and Niemann-Pick type A (NB-A) and B (NP-B), very high levels are usually seen [Guo et al 1995;Wajner et al 2004]. The presence of elevated chitotriosidase would have to be paired with (hepato)splenomegaly and normal activities Although clinically heterogeneous, several 'red flag' signs and symptoms exist, which should alert clinicians towards suspecting and investigating for the presence of the disorder.…”

“…of acid sphingomyelinase (excluding NP-A and NP-B) and β-glucocerebrosidase (excluding GD), for NP-C to be further considered [McKay Bounford and Gissen, 2014]. In addition, 10% of the population has a pseudodeficiency mutation, which makes this test uninterpretable [Ries et al 2006].…”

“…Despite its promise as a diagnostic tool, genetic sequencing sometimes identifies mutations clearly associated with disease on only one allele or provides negative results [Vanier, 2010;Bauer et al 2013], even in patients where there is strong clinical suspicion and/or supportive biochemical test results pointing towards NP-C. Additionally, many families have 'private' sequence variants that have not been reported/published elsewhere [McKay Bounford and Gissen, 2014]. Hence, in a number of suspected patients, confirmation of a diagnosis is not possible through genetic sequencing alone.…”