Niemann-Pick disease is a group of rare inherited disorders in which fatty substances build up inside cells because the body can’t properly break them down or move them. This accumulation damages cells in the brain, liver, spleen, lungs, and bone marrow, leading to progressive organ failure and neurological decline. The disease affects roughly 0.35 to 2.2 per 100,000 births worldwide, depending on the country and the specific type.
The Three Main Types
Niemann-Pick disease comes in three forms, grouped by their underlying genetic cause. Types A and B both stem from mutations in the same gene (SMPD1), which provides instructions for making an enzyme that breaks down a specific fat called sphingomyelin. Without enough of this enzyme, sphingomyelin piles up inside lysosomes, the tiny recycling centers within cells. Over time, these bloated cells lose the ability to function normally. The key difference between types A and B is severity: type A is the most devastating form, appearing in infancy and progressing rapidly, while type B develops later and advances more slowly.
Type C is a fundamentally different disease at the cellular level, though it shares a name. It’s caused by mutations in one of two other genes (NPC1 or NPC2) that produce proteins responsible for shuttling cholesterol out of lysosomes. Normally, these two proteins work like a relay team: one picks up cholesterol inside the lysosome and hands it off to the other, which transports it across the lysosome membrane so the cell can use it. When either protein is missing or broken, cholesterol and other fats get trapped inside lysosomes and accumulate in the liver, spleen, and brain.
How Each Type Affects the Body
Type A: Infantile Neurovisceral
Type A is the most severe form. Symptoms appear within the first few months of life and include an enlarged liver and spleen, feeding difficulties, and loss of early motor skills. Neurological decline is rapid and relentless. Children with type A rarely survive past early childhood, and there is currently no approved treatment that addresses the brain involvement in this form.
Type B: Chronic Visceral
Type B primarily affects organs outside the brain. The liver and spleen enlarge significantly, and the lungs can become involved, causing breathing difficulties. Bone marrow fills with lipid-laden cells called foam cells, which can affect blood counts. Many people with type B reach adulthood, though the disease still shortens life expectancy and progressively limits organ function. Neurological symptoms are generally absent or minimal in this form.
There is also an intermediate form, sometimes called type A/B, which falls between the two. People with this form experience some neurological involvement, but it progresses more slowly than in type A.
Type C: Chronic Neurovisceral
Type C is the most variable. It can appear at any age, from the newborn period through adulthood, and the age when neurological symptoms begin largely determines how the disease will progress. Common symptoms include difficulty walking and increasing clumsiness, trouble swallowing, slurred speech, muscle weakness, and cognitive decline. An enlarged liver and spleen often appear first, sometimes years before any neurological signs.
Life expectancy in type C depends heavily on when symptoms start. In a UK study of 74 patients, children who developed neurological symptoms before 18 months typically did not survive past age 5. Those with late-infantile onset lived to an average of about 13 years, while juvenile-onset patients survived to roughly 26 years on average. People whose symptoms first appeared in adolescence or adulthood had a mean age of death around 34, though individual outcomes vary considerably.
Getting a Diagnosis
Niemann-Pick disease is often suspected when a child or adult presents with an unexplained enlarged liver and spleen, particularly when combined with neurological symptoms. For types A and B, the diagnosis can be confirmed by measuring the activity of acid sphingomyelinase in a blood sample or skin biopsy. Low enzyme activity points directly to the disease. Genetic testing of the SMPD1 gene can then identify the specific mutations involved.
Type C requires a different diagnostic approach because the enzyme deficiency isn’t the problem. A skin biopsy can be used to grow cells in the lab and test how they handle cholesterol, looking for the characteristic pattern of cholesterol trapped in lysosomes. Genetic testing of the NPC1 and NPC2 genes confirms the diagnosis. Because symptoms of type C overlap with many other neurological conditions, diagnosis is frequently delayed, sometimes by years.
Available Treatments
For most of the disease’s history, treatment was limited to managing symptoms. That has begun to change, though options remain limited.
For types A/B and B, the FDA has approved an enzyme replacement therapy called olipudase alfa (brand name Xenpozyme). It works by supplying the missing enzyme through regular intravenous infusions, allowing cells to break down the accumulated sphingomyelin. Clinical trials in both adults and children with types B and A/B showed improvements in organ size and lung function. The treatment does not cross into the brain, so it addresses only the non-neurological symptoms. For type A, the most severe infantile form, no therapeutic benefit has been documented.
For type C, the FDA approved arimoclomol (brand name Miplyffa) in 2024, the first treatment specifically indicated for this form. It’s an oral medication used in combination with another drug called miglustat, and it’s approved for adults and children age 2 and older. In clinical trials, the combination slowed the progression of key neurological symptoms, including walking ability, speech, swallowing, and fine motor skills, compared to placebo. While not a cure, this represents a meaningful shift from purely supportive care to a treatment that can slow the disease’s trajectory.
Inheritance and Carrier Risk
All forms of Niemann-Pick disease are inherited in an autosomal recessive pattern. This means a child must receive a defective copy of the relevant gene from both parents to develop the disease. Parents who each carry one mutated copy are typically healthy and unaware of their carrier status. When two carriers have a child, there is a 25% chance with each pregnancy that the child will inherit both defective copies and develop the condition.
Certain populations carry higher rates of specific mutations. Type A, for example, occurs more frequently among people of Ashkenazi Jewish descent. Genetic counseling and carrier testing are available for families with a known history of the disease or those in higher-risk populations. Prenatal and newborn testing can also identify affected individuals early, which is increasingly important now that treatments exist for some forms.