Niemann-Pick Type C (NPC) is a rare genetic disease in which the body loses its ability to move cholesterol and other fats out of cells, causing them to build up to toxic levels in the brain, liver, spleen, and lungs. It affects roughly 1 in 89,000 live births and is progressive, meaning symptoms worsen over time. NPC is often called a “lysosomal storage disorder” because the buildup happens inside lysosomes, the recycling compartments within every cell.
How NPC Disrupts Cells
Inside healthy cells, cholesterol arrives packaged in particles that get broken down in the lysosome. Two proteins, called NPC1 and NPC2, work as a relay team: NPC2 grabs the freed cholesterol and hands it off to NPC1, which then shuttles it out of the lysosome so the cell can use it. In people with NPC, mutations in either the NPC1 or NPC2 gene break this handoff. About 95% of cases stem from NPC1 mutations.
When cholesterol can’t exit the lysosome, it piles up alongside other fatty substances called glycosphingolipids. This accumulation damages cells throughout the body but is especially destructive in the brain, liver, and spleen. The progressive loss of brain cells is what drives most of the disease’s neurological symptoms and ultimately determines life expectancy.
Symptoms by Age of Onset
NPC can appear at almost any age, from the first days of life through the sixth or seventh decade. The age when neurological symptoms begin is the single most important factor in predicting how the disease will progress. Generally, earlier onset means faster decline.
Infants and Young Children
In newborns and infants, the first signs are usually jaundice, an enlarged liver, an enlarged spleen, or both. These organ symptoms typically show up before any neurological problems. Some infants develop severe liver or lung disease within the first months of life. Children who develop neurological symptoms before 18 months often do not survive past age 5.
Older Children and Adolescents
In the late-infantile and juvenile forms, clumsiness and difficulty walking (ataxia) tend to appear first, followed by trouble with speech and swallowing. Cognitive decline may initially look like a learning disability. A UK study of 74 patients found that the mean age of death for the late-infantile group was about 13 years, while for the juvenile-onset group it was roughly 26 years.
Adults
Adult-onset NPC is the rarest and most easily missed form. It can present with psychiatric symptoms like psychosis or cognitive decline that mimic other conditions, alongside movement problems such as ataxia or dystonia. About half of adult patients have little or no liver or spleen enlargement, which makes the disease harder to suspect. When neurological symptoms begin after age 11, 64% of patients are still alive after 10 years of follow-up. The mean age of death in the adolescent/adult group is around 34 years, though some individuals live considerably longer.
The Eye Movement Sign
One of the earliest and most characteristic clues to NPC is difficulty moving the eyes vertically, particularly downward. This starts subtly as slowed vertical eye movements and can progress to a complete inability to look up or down voluntarily. It is sometimes the only neurological sign in adults for years before other symptoms appear. Neurologists test for this specifically when NPC is suspected, and its presence alongside ataxia or cognitive decline strongly points toward the diagnosis.
How NPC Is Diagnosed
Diagnosing NPC has historically been slow and difficult. For decades, the standard test required a skin biopsy: doctors grew skin cells in a lab and stained them with a dye called filipin to reveal cholesterol buildup inside lysosomes. This test cost around $3,000, took about three months to get results, and was only available at specialized centers. Worse, it missed more than a third of cases that had atypical cholesterol patterns in their cells.
A simpler blood test has largely replaced filipin staining as the first screening step. It measures a cholesterol byproduct called cholestane-triol, which is elevated in NPC patients. The test is faster and more accessible, though it isn’t perfect: triol levels can also be high in a few other metabolic conditions, and about 25% of people who carry one copy of the gene (carriers, not affected) have levels that overlap with actual patients. Because of these limitations, genetic sequencing of the NPC1 and NPC2 genes is used to confirm the diagnosis.
Treatment Options
There is no cure for NPC, but three medications are now available that target different aspects of the disease.
- Miglustat is approved in Europe for NPC. It works by reducing the production of glycosphingolipids, the fatty substances that accumulate alongside cholesterol. In clinical studies, patients on miglustat showed stabilization or improvement in walking ability, swallowing, cognitive function, and eye movements over one year. It is taken by mouth, typically three times daily.
- Miplyffa (arimoclomol) was approved by the FDA for adults and children aged 2 and older. It boosts the activity of heat shock proteins, which are the cell’s built-in repair crew. These proteins help stabilize lysosomal membranes and improve the processing of the NPC1 protein itself, addressing some of the underlying cellular dysfunction.
- Aqneursa was also approved by the FDA to treat the neurological symptoms of NPC in patients weighing at least 15 kilograms (about 33 pounds). It works by correcting energy production problems in cells, improving how mitochondria and lysosomes function. This helps reduce cholesterol and lipid buildup and may also lower brain inflammation.
Beyond these medications, treatment involves managing individual symptoms. Physical therapy helps maintain mobility, speech therapy addresses swallowing and communication difficulties, and psychiatric care may be needed for patients with mood or psychotic symptoms.
Why Diagnosis Is Often Delayed
NPC is frequently misdiagnosed or overlooked for years, particularly in older children and adults. The neurological symptoms overlap with many more common conditions. A child with declining school performance and clumsiness might be evaluated for ADHD or a learning disorder. An adult with psychosis might receive a psychiatric diagnosis for years before anyone considers a metabolic cause. The rarity of the disease means most physicians will never encounter a case in their careers.
The combination of vertical gaze problems with ataxia, cognitive decline, or an enlarged spleen is the clinical pattern that should trigger testing. Awareness of this pattern is the single biggest factor in shortening the diagnostic delay, which matters because earlier treatment has a better chance of preserving neurological function before irreversible damage occurs.
Genetics and Inheritance
NPC follows an autosomal recessive inheritance pattern, meaning a child must inherit a defective copy of the NPC1 or NPC2 gene from each parent. Parents who each carry one mutated copy are typically healthy and unaware of their carrier status. When both parents are carriers, each pregnancy has a 25% chance of producing an affected child. Genetic counseling is recommended for families with a confirmed case.