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

Background: Niemann-Pick type C (NPC) is a treatable genetic disorder, mainly characterized by neurological dysfunction and liver damage. Its diagnosis is based on an invasive test which requires a skin biopsy to demonstrate the cholesterol accumulation in culture fibroblasts of affected patients. In the last years, new biomarkers have been investigated aiming to facilitate the diagnosis and screening of NPC; two of these possible candidates are the oxysterol cholestane-3 beta,5 alpha,6 beta-triol (triol), a product of non-enzymatic oxidation of cholesterol, and the enzyme chitotriosidase (CT), a fully active chitinase (EC-3.2.1.14) synthesized by activated macrophages. Methods: In this work, we investigated the potential use of the combined analysis of triol levels and CT activity for diagnosis, screening and monitoring of NPC in Brazilian patients, correlating with the results of Filipin staining and genetic analysis. We studied 122 untreated individuals with clinical suspicion of NPC who were separated in two groups according their concentrations of triol (higher or lower than the cutoff value of 100 ng/mL). We also analyzed blood samples from 5 patients with previous diagnosis of NPC who were under treatment with miglustat Results: The results of this work demonstrated that patients with higher concentrations of triol (group A) also presented a high activity of CT and most of them had also a positive Filipin test. Two patients of this group presented an inconclusive Filipin test, being one eventually diagnosed as NPC by molecular investigation and the other eventually diagnosed as Niemann-Pick type A or B (NPA/B) by the low acid sphingomyelinase activity presented. Three patients with high triol concentrations who had a negative result in the Filipin test presented low activities of acid sphingomyelinase, being diagnosed as NPA/B. On the other hand, triol concentrations were normal in NPC patients treated with miglustat, although CT activity in these individuals remained abnormal. In the patients with triol lower than 100 ng/mL (group B), most presented a normal activity of CT. No patient of this group had a positive Filipin test and the few patients with inconclusive Filipin test did not present pathogenic mutations in the NPC1 or NPC2 genes. Conclusions: In conclusion, our data demonstrated that the combined analysis of triol and CT is quite sensitive and specific for the identification of NPC patients. Although the number of analysis in NPC patients treated with miglustat was small, the data indicate that the measurement of triol could also be potentially useful for treatment monitoring. (C) 2016 Elsevier B.V. All rights reserved.