Diagnosis of Niemann-Pick disease type C with 7-ketocholesterol screening followed by NPC1/NPC2 gene mutation confirmation in Chinese patients

Abstract

BackgroundIt has been reported that oxidation product of cholesterol, 7-ketocholesterol, increases in plasma of patients with NP-C. Previously, we established a rapid test to determine the plasma 7-ketocholesterol level and found it elevated significantly in patients with acid sphingomyelinase deficient NPD and NP-C disease.MethodsIndividuals randomly referred to our outpatient clinics in the past two years for hepatosplenomegaly or isolated splenomegaly, who have been excluded as acid sphingomyelinase deficient NPD or Gaucher disease, and individuals with newborn cholestasis, psychomotor regression/retardation, were screened for plasma 7-ketocholesterol level. Individuals with high 7-ketocholesterol level were then analyzed for NPC1 and NPC2 gene mutation to confirm the accuracy of NP-C diagnosis.ResultsBy screening the plasma 7-ketocholesterol of suspect individuals, 12 out of 302 (4%) had shown remarkable high levels compared with reference. All these twelve individuals were subsequently confirmed to be NP-C by DNA analysis of NPC1 and NPC2 genes, with the early infantile form (n = 7), the late infantile form (n = 1), the juvenile form (n = 1) and the adult form (n = 1). Furthermore, two NP-C patients without observable neuropsychiatric disability were picked up through this procedure. Only one patient had NP-C due to NPC2 gene mutations, with the rest due to NPC1 gene mutations. We found that in NP-C patients AST was usually mildly elevated and ALT was in a normal range when jaundice was not present. In total, 22 mutant alleles were identified in the NPC1 gene, including six novel small deletions/insertions, e.g., c.416_417insC, c.1030delT, c.1800delC, c.2230_2231delGT, c.2302_2303insG, and c.2795dupA; seven novel exonic point mutations, c.1502A>T (p.D501V), c.1553G>A (p.R518Q), c.1832A>G (p.D611G), c.2054T>C (p.I685T), c.2128C>T(p.Q710X), c.2177G>C (p.R726T), c.2366G>A (p.R789H), and one novel intronic mutation c.2912-3C>G. Small deletions/insertions constituted nearly half of the mutant alleles (10/22, 45%), indicating a unique mutation spectrum in this cohort of Chinese NP-C patients.ConclusionOur data confirm in a clinical setting that screening plasma 7-ketocholesterol is an efficient and practical diagnostic tool to identify NP-C patients from suspect individuals. Patients without neuropsychological involvement could also be identified by this method therefore allowing an opportunity for earlier treatment.

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

“…In this context, previous studies implicating oxidative stress in NPC disease pathogenesis raised the possibility that non-enzymatic formation of cholesterol oxidation products could serve as disease biomarkers [3]. Since Porter et al in 2010 [17] published increased levels of plasma oxysterols in NPC1 patients, which were also correlated with age of disease onset and disease severity, new methods of measuring these metabolites began to be investigated [13,23,32,33]. Early detection of NPC disease by an oxysterol-based newborn screening test would facilitate diagnosis in presymptomatic NPC subjects.…”

Cholestane-3β,5α,6β-triol: high levels in Niemann-Pick type C, cerebrotendinous xanthomatosis, and lysosomal acid lipase deficiency

“…Therefore, it is desirable to have the concurrence of other methods or other biomarkers to help the diagnosis of this disease. Recent studies have shown that plasma CT and 7-KC could be potential biomarkers for the diagnosis of NPC patients (8)(9)(10)(11)(12)(13). We aimed to determine the sensitivity and specifi city of these biomarkers for the diagnosis of NPC compared with patients suffering from other lysosomal, peroxisomal, or sterol disorders, or other patients with hepatic or neurological alterations, as well as patients with familial hypercholesterolemia.…”

“…In the NPC murine model, an increase of two oxysterols, cholestane-3 b ,5 a ,6 b -triol (CT) and 7-ketocholesterol (7-KC), has been observed ( 8 ). This evidence was later confi rmed in NPC patients (8)(9)(10)(11)(12)(13), showing a correlation between the oxysterol profi le and the age of onset and severity of the disease ( 8,14 ). Moreover, CT specifi cally has been found to be increased in NPC disease compared with other lysosomal and neurodegenerative diseases ( 8 ).…”

Plasma lysosphingomyelin demonstrates great potential as a diagnostic biomarker for Niemann–Pick disease type C in a retrospective study

“…Pre-specified populations with sufficient suspicion of NP-C would include infants with neonatal cholestatic liver disease [2], patients with hepatosplenomegaly [31], the intellectually disabled [32] and adults with neurological and psychiatric symptoms [4]. Together with differential clinical diagnosis, the standard enzymatic tests for Gaucher and NP-A/ B could also be used as an alternative to sequencing to differentiate these disorders from NP-C in patients with elevated plasma SPC and GlcSph.…”