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Condition report · Metabolic

Niemann-Pick Disease Type C

Whole genome sequencing evaluates SMPD1 (types A and B) and NPC1/NPC2 (type C) simultaneously, identifying treatable NPC1/NPC2 variants in adults presenting with vertical gaze palsy, cerebellar ataxia, or early-onset cognitive decline.

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About this condition

NPC is a complex lipid storage disease mainly characterized by the accumulation of unesterified cholesterol in the late endosomal/lysosomal compartment.

Niemann-Pick disease (NPD) encompasses genetically and clinically distinct lysosomal storage disorders. Types A and B are caused by pathogenic variants in SMPD1 (sphingomyelin phosphodiesterase 1) on chromosome 11p15.4, encoding acid sphingomyelinase; their deficiency causes sphingomyelin accumulation in macrophages of the liver, spleen, lung, and brain. Type A is a severe infantile neurodegenerative condition with death by age 3; type B is an attenuated form with primarily visceral involvement and variable neurological features, with survival into adulthood. Type C Niemann-Pick disease is caused by variants in NPC1 (95%) or NPC2 (5%) on different chromosomes (these encode proteins mediating intracellular cholesterol transport) and is pathophysiologically and clinically distinct from types A and B.

Niemann-Pick type C (NPC) is arguably the most diagnostically challenging lysosomal storage disorder. In the adolescent and adult-onset forms (which account for approximately 50% of all NPC cases), the presentation mimics common neurological and psychiatric conditions: vertical supranuclear gaze palsy (VSGP, a nearly pathognomonic finding for NPC but often unrecognized), cerebellar ataxia, dystonia, dysarthria, dysphagia, cognitive decline, and psychiatric symptoms including psychosis, depression, and anxiety. The mean time from symptom onset to NPC diagnosis in adolescent/adult-onset cases is approximately 4-7 years, during which patients may receive misdiagnoses of multiple sclerosis, spinocerebellar ataxia, bipolar disorder, or schizophrenia.

Miglustat (Zavesca), a substrate reduction therapy, is approved in Europe for NPC neurological stabilization; it slows the rate of neurological progression and is most effective when initiated early in the disease course. Arimoclomol, a heat shock protein amplifier, is in late-stage clinical development for NPC. These disease-modifying therapies make molecular diagnosis of NPC directly therapeutic: a confirmed NPC1 or NPC2 pathogenic variant qualifies the patient for miglustat and for arimoclomol trial enrollment. In types A/B, olipudase alfa (Xenpozyme), an enzyme replacement therapy, was approved for non-neurological manifestations of acid sphingomyelinase deficiency in 2022.

Very late-onset NPC (age >40) may present as an atypical dementia or frontotemporal dementia-like syndrome. NPC should be considered in any adult under 60 with vertical gaze palsy, unexplained cerebellar ataxia, or early cognitive decline accompanied by splenomegaly.

The condition we analyse

Autosomal recessive

NPC is a complex lipid storage disease mainly characterized by the accumulation of unesterified cholesterol in the late endosomal/lysosomal compartment.

What a diagnosis changes

NPC: miglustat (Zavesca, EU approved); arimoclomol (in clinical trials); Types A/B: olipudase alfa (Xenpozyme, 2022 approval for non-neurological manifestations); supportive care; miglustat prior to molecular confirmation may be considered given the diagnostic difficulty

Genes analysed

Also known as

NPC

Includes 7 related subtypes ↓
  • Niemann-Pick disease type C, adult neurologic onset
  • Niemann-Pick disease type C, juvenile neurologic onset
  • Niemann-Pick disease type C, late infantile neurologic onset
  • Niemann-Pick disease type C, severe early infantile neurologic onset
  • Niemann-Pick disease type C, severe perinatal form
  • Niemann-Pick disease, type C1
  • Niemann-Pick disease, type C2
MONDO:0018982Orphanet 646MedGen 67399

Why whole genome sequencing

SMPD1 and NPC1/NPC2 are distinct genes requiring different tests. Plasma oxysterol biomarkers screen for NPC but are not specific; molecular confirmation requires complete NPC1 and NPC2 sequencing. Whole genome sequencing evaluates all Niemann-Pick genes simultaneously.

Vertical gaze palsy in a young adult is virtually pathognomonic for NPC, but NPC confirmation requires molecular testing

Vertical supranuclear gaze palsy (reduced or absent voluntary vertical eye movement) is the single most distinctive clinical feature of NPC and is rarely seen in other conditions. Combined with cerebellar ataxia, cognitive decline, and a history of prolonged neonatal jaundice or childhood splenomegaly, it should prompt immediate NPC evaluation. Plasma oxysterol measurement (24S-hydroxycholesterol, 25-hydroxycholesterol, 7-ketocholesterol) provides a sensitive screening biomarker but is not specific. Confirmatory molecular diagnosis requires complete sequencing of NPC1 (42 exons) and NPC2, genes that have no hotspot and require full-gene analysis. Whole genome sequencing provides this simultaneously.

Miglustat therapy requires confirmed molecular diagnosis, and should begin as early in NPC neurological disease as possible

Miglustat's effect in NPC is one of slowing progression; it does not reverse neurological damage already sustained. Clinical trial data and registry studies consistently show that earlier initiation of miglustat therapy in the neurological disease course is associated with better preservation of neurological function. Every year of diagnostic delay in adult-onset NPC is a year of neurological damage accumulation before treatment can begin. Confirming the NPC1 or NPC2 molecular diagnosis is the prerequisite for miglustat initiation; a symptom-based diagnosis alone is not sufficient for drug approval in most jurisdictions. Whole genome sequencing reduces time to molecular confirmation.

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