What is the mnemonic for Niemann-Pick disease?

A simple mnemonic is FOAMY: foam cells (lipid-laden macrophages), organomegaly (hepatosplenomegaly), acid sphingomyelinase deficiency with sphingomyelin storage, macular cherry-red spot, and young death in type A. It covers types A, A/B and B, now called acid sphingomyelinase deficiency (ASMD). The classic enzyme hook is "No man picks his nose with his sphinger." Type C is a separate cholesterol-transport disease: think vertical gaze palsy, ataxia and gelastic cataplexy.

What are foam cells in Niemann-Pick disease?

Foam cells, also called Niemann-Pick cells, are macrophages filled with lipid they cannot break down, mainly sphingomyelin and cholesterol. Many small vacuoles give their cytoplasm a foamy look. They collect in bone marrow, spleen, liver, lymph nodes and lungs, sometimes beside sea-blue histiocytes, while Gaucher cells look like wrinkled paper instead. Foam cells are not specific: they also occur in type C, acid lipase deficiency and atherosclerotic plaque, so diagnosis rests on enzyme, biomarker and genetic tests.

How do you tell Niemann-Pick disease from Tay-Sachs disease?

Both can cause a cherry-red spot and neurodegeneration in infancy, and both are more common in Ashkenazi Jewish families. Check the abdomen: Niemann-Pick type A enlarges the liver and spleen by about 3 months and brings lung disease and foam cells, while in Tay-Sachs the liver and spleen are normal-sized. Tay-Sachs is hexosaminidase A deficiency with GM2 ganglioside storage and an exaggerated startle. Sandhoff disease is the Tay-Sachs look-alike that does enlarge the liver.

What is the difference between Niemann-Pick type A, type B and type C?

Types A and B are forms of acid sphingomyelinase deficiency caused by SMPD1 variants. Type A, the infantile neurovisceral form, brings massive hepatosplenomegaly, lung disease, a cherry-red spot, regression and death usually before age 3. Type B, the chronic visceral form, brings hepatosplenomegaly, interstitial lung disease, low platelets and low HDL without progressive brain disease; most reach adulthood. Type C is a different disease of NPC1 or NPC2 cholesterol transport, with ataxia, vertical supranuclear gaze palsy and cataplexy.

What enzyme is deficient in Niemann-Pick disease, and what builds up?

In types A, A/B and B, acid sphingomyelinase, encoded by SMPD1, is deficient. It normally splits sphingomyelin into ceramide and phosphocholine inside lysosomes, so sphingomyelin builds up, followed by cholesterol and lyso-sphingomyelin, mainly in macrophages of the liver, spleen, bone marrow and lungs. Type C involves no enzyme deficiency: the NPC1 or NPC2 transport proteins fail, so unesterified cholesterol, glucosylceramide and gangliosides accumulate in lysosomes. All forms are autosomal recessive.

What is the treatment for Niemann-Pick disease?

For acid sphingomyelinase deficiency, olipudase alfa (Xenpozyme), an intravenous enzyme replacement approved by the FDA in 2022, treats non-central nervous system manifestations such as organ enlargement, lung disease and low platelets, but not type A brain disease. For type C, the FDA approved arimoclomol (Miplyffa), used with miglustat from age 2, and levacetylleucine (Aqneursa), for patients weighing at least 15 kg, in 2024. Miglustat alone is not FDA-approved for type C.

Niemann-Pick Disease Mnemonic: Types A/B vs C, Foam Cells

The Niemann-Pick mnemonic is FOAMY: Foam cells (lipid-laden macrophages), Organomegaly (hepatosplenomegaly), Acid sphingomyelinase deficiency storing sphingomyelin (types A and B, autosomal recessive), Macular cherry-red spot and Young death in type A. Type C is a different disease: NPC1 or NPC2 variants trap cholesterol in lysosomes, causing ataxia, vertical supranuclear gaze palsy and cognitive decline.

The classic review-book hook still works for the enzyme: "No man picks his nose with his sphinger" (Niemann-Pick, sphingomyelinase). The classic exam separator is the abdomen: Niemann-Pick type A and Tay-Sachs both give an infant a cherry-red spot and regression, but only Niemann-Pick A enlarges the liver and spleen.

Current names: types A, A/B and B are now acid sphingomyelinase deficiency (ASMD), caused by SMPD1 variants. Niemann-Pick type C (NPC) shares the name and the foam cells but is a cholesterol-trafficking disorder with its own genes, tests and FDA-approved drugs.

FOAMY: the Niemann-Pick mnemonic, decoded

Letter	Stands for	What to remember
F	Foam cells	Lipid-laden macrophages ("Niemann-Pick cells") in marrow, spleen, liver and lungs; sea-blue histiocytes may sit beside them
O	Organomegaly	Hepatosplenomegaly by about 3 months in type A, later massive; splenomegaly is often the first sign of type B
A	Acid sphingomyelinase	SMPD1, autosomal recessive; sphingomyelin is not split into ceramide and phosphocholine; type A is more common in Ashkenazi Jewish families
M	Macular cherry-red spot	Eventually in every untreated type A infant; up to a third of people with type B have one (or a macular halo) without brain disease
Y	Young death in type A	Development stalls by 10 to 12 months, then regresses; most untreated children die before age 3, usually of respiratory causes; people with type B usually reach adulthood

The C's of type C

C	Meaning
Cholesterol stuck	NPC1 (about 95%) or NPC2 variants block lysosomal export of LDL-derived cholesterol; glycolipids pile up too
Can't look up or down	Vertical saccades slow first (children compensate by blinking or thrusting the head), then vertical supranuclear gaze palsy
Cataplexy	Gelastic cataplexy, a sudden loss of muscle tone triggered by laughter, in about 20% of children
Cerebellar ataxia	Clumsiness and falls, then dysarthria and dysphagia; childhood-onset disease is usually fatal (aspiration pneumonia) by the late teens or twenties
Cognitive and psychiatric decline	School problems often mistaken for attention-deficit disorder; psychosis, depression or early dementia in adults
Cholestatic jaundice	Prolonged neonatal jaundice, fetal ascites or isolated splenomegaly can come first, but many patients never have organomegaly

NPC's old name, DAF syndrome (downgaze paralysis, ataxia, foam cells), is a second ready-made mnemonic.

Niemann-Pick foam cells: what they are and where they show up

Foam cells are macrophages stuffed with lipid they cannot digest. Macrophages suffer most because they are actively phagocytic and packed with lysosomes; stored sphingomyelin drags cholesterol and other lipids in with it. The cells can reach 90 micrometers across; many small vacuoles make the cytoplasm look foamy, and electron microscopy shows dense, concentrically laminated inclusions.

Where they are seen:

Bone marrow, the classic exam image: in a 2024 French series, all 14 diagnostic marrow smears from patients with ASMD or NPC showed numerous foamy histiocytes, often clustered.
Spleen, liver and lymph nodes, which they infiltrate throughout, causing hepatosplenomegaly.
Lungs, in the alveoli and interstitium, causing interstitial lung disease and repeated infections.

Sea-blue histiocytes are macrophages packed with ceroid or lipofuscin granules that stain blue or blue-green with May-Grünwald-Giemsa; the granules are usually PAS-positive and autofluorescent. In the French series they appeared mainly in ASMD type B, always beside ordinary foam cells, but that series had only two NPC marrows; Orphanet says both usually occur in NPC marrow, and "sea-blue histiocytosis" is one of NPC's old names.

Neither cell is specific. Similar foamy macrophages occur in lysosomal acid lipase deficiency (Wolman disease, cholesteryl ester storage disease), GM1 gangliosidosis and Tangier disease, and foam cells are the hallmark of atherosclerotic fatty streaks: intimal macrophages that took up modified LDL through scavenger receptors. Sea-blue histiocytes also appear in thalassemia, sickle cell disease, chronic myeloid leukemia, lymphoma, immune thrombocytopenia and parenteral nutrition.

Feature	Niemann-Pick foam cell	Sea-blue histiocyte	Gaucher cell
Seen in	ASMD (all types) and NPC	ASMD and NPC; also many acquired conditions	Gaucher disease; look-alike pseudo-Gaucher cells in myeloproliferative and myelodysplastic disorders
Cytoplasm	Many small vacuoles (white, pale blue or pink on Giemsa-type stains)	Blue or blue-green ceroid or lipofuscin granules, usually PAS-positive and autofluorescent	Wrinkled paper ("crumpled tissue paper"), PAS-positive
Stored material	Sphingomyelin plus cholesterol (ASMD); cholesterol and glycosphingolipids (NPC)	Ceroid or lipofuscin	Glucocerebroside

Morphology never makes the diagnosis. Gaucher cells can be mistaken for foam cells on Giemsa staining, and marrow examination is not needed to diagnose ASMD: confirm it with an enzyme assay plus SMPD1 testing (Gaucher disease with glucocerebrosidase activity or GBA1 testing). The Gaucher side is drawn in the Gaucher disease sketch.

Tay-Sachs vs Niemann-Pick: check the liver and spleen

Both can give an infant a cherry-red spot and neurodegeneration, and both are more common in Ashkenazi Jewish families. Memory aid: Niemann-Pick picks up the organs; Tay-Sachs spares them.

Feature	Tay-Sachs (infantile)	Niemann-Pick type A (infantile neurovisceral ASMD)
Deficient enzyme (gene)	Hexosaminidase A (HEXA)	Acid sphingomyelinase (SMPD1)
Stored lipid	GM2 ganglioside, mainly in neurons	Sphingomyelin, mainly in macrophages, plus neurons
Liver and spleen	Normal size	Enlarged by about 3 months, later massive
Lungs	Not typical	Interstitial lung disease, frequent infections
Neurologic course	Loss of motor skills from 3 to 6 months; exaggerated startle; seizures near 12 months; macrocephaly from 18 months	Signs from a median of 7 months; development stalls by 10 to 12 months; hypotonia, lost reflexes
Cherry-red spot	Virtually all infants	Eventually all untreated infants
Histology	Ballooned neurons; whorled "onion-skin" lysosomes on electron microscopy	Foam cells in marrow, spleen, liver and lungs
Untreated outcome	Death usually between ages 2 and 5	Death usually before age 3

Two exceptions to the rule: Sandhoff disease (hexosaminidase A and B) follows the Tay-Sachs course but adds hepatomegaly and bone changes and has no ethnic association, and GM1 gangliosidosis can pair a cherry-red spot with hepatosplenomegaly, coarse facies and skeletal disease. Tay-Sachs gets its own drill in the Tay-Sachs 5-second rule.

Sphingolipidoses mnemonic: where Niemann-Pick fits

Ask three questions of every sphingolipidosis: which enzyme, which lipid, and is the abdomen big?

Disease	Deficient enzyme	Stored lipid	Liver and spleen	Hook
Niemann-Pick A/B	Acid sphingomyelinase	Sphingomyelin	Enlarged	FOAMY; foam cells, lung disease
Tay-Sachs	Hexosaminidase A	GM2 ganglioside	Normal	Cherry-red spot, exaggerated startle
Sandhoff	Hexosaminidase A and B	GM2 ganglioside	Liver enlarged	Tay-Sachs plus viscera and bone
Gaucher	Glucocerebrosidase	Glucocerebroside	Enlarged	Wrinkled-paper macrophages, bone crises, Erlenmeyer flask
Krabbe	Galactocerebrosidase	Galactocerebroside, psychosine	Not typical	Globoid cell leukodystrophy, extreme irritability
Metachromatic leukodystrophy	Arylsulfatase A	Sulfatides	Not typical	Central and peripheral demyelination, gait problems
Fabry	α-Galactosidase A	Globotriaosylceramide	Not typical	X-linked; painful crises, angiokeratomas, kidney and heart disease

All are autosomal recessive except Fabry, which is X-linked. Every enzyme step is mapped in the sphingolipidoses table; for the rest, see Krabbe disease and Fabry disease.

I-cell disease is the classic look-alike, not a sphingolipidosis. In mucolipidosis II, GNPTAB variants knock out N-acetylglucosamine-1-phosphotransferase, so lysosomal enzymes miss their mannose-6-phosphate "address tag" and are secreted instead of reaching lysosomes (their plasma levels run 5 to 20 times normal). Expect skeletal deformities at birth, coarse facies and gingival hypertrophy in infancy, joint contractures and death in early childhood.

ASMD vs NPC: current names, mechanism and genetics

Old label	Current name	Gene (locus)	Defect	Main stored lipid
Type A	Infantile neurovisceral ASMD	SMPD1 (11p15.4)	Acid sphingomyelinase (enzyme)	Sphingomyelin
Type A/B	Chronic neurovisceral ASMD	SMPD1	Acid sphingomyelinase	Sphingomyelin
Type B	Chronic visceral ASMD	SMPD1	Acid sphingomyelinase	Sphingomyelin
Type C (C1, C2)	Niemann-Pick disease type C	NPC1 (18q11.2) or NPC2 (14q24.3)	Cholesterol transport proteins, not enzymes	Unesterified cholesterol, glucosylceramide, gangliosides

The ASMD subtypes are points on one continuum. Type C was named alongside them in 1961 but is a different disease.

ASMD: acid sphingomyelinase splits sphingomyelin into ceramide and phosphocholine in lysosomes. Without it, sphingomyelin builds up, followed by cholesterol and lyso-sphingomyelin, mostly in macrophages.
NPC: cholesterol released from endocytosed LDL in the lysosome is bound by soluble NPC2 and handed to membrane-bound NPC1 for export; losing either protein traps it (see lipoprotein metabolism).
Cherry-red spot: lipid-swollen retinal ganglion cells whiten the macula, but the center of the fovea has no ganglion cells, so the red choroid shows through.

Genetics: every form is autosomal recessive, so carrier parents face a 25% risk in each pregnancy (see autosomal recessive inheritance). ASMD affects about 1 in 250,000 people and is pan-ethnic; three SMPD1 variants cause about 90% of type A alleles in Ashkenazi Jewish families, and one copy of p.Arg610del protects against neurologic disease. NPC affects about 1 in 100,000 live births, about 95% from NPC1, with founder variants in Nova Scotia Acadians (the old "type D") and an Israeli Bedouin group. Carrier testing uses the family's variants (enzyme activity is unreliable for ASMD carriers); prenatal testing can also use enzyme activity.

Presentation by type

Feature	ASMD type A	ASMD type A/B	ASMD type B
Onset	Hepatosplenomegaly at 2 to 4 months	Variable; neurologic signs later than in type A	Childhood to adulthood
Viscera	Massive hepatosplenomegaly, liver dysfunction, failure to thrive, interstitial lung disease	Variable, as in type B	Splenomegaly, hepatomegaly, interstitial lung disease, thrombocytopenia, liver fibrosis, osteopenia, growth delay; low HDL with high triglycerides and LDL
Brain and eye	Developmental arrest, progressive hypotonia; cherry-red spot	Slowly progressive ataxia, learning problems, peripheral neuropathy	No progressive neurologic disease; cherry-red spot or halo in up to a third
Outlook untreated	Death typically by 3 years	Most reach adulthood	Usually well into adulthood; lung and liver disease are leading causes of death

NPC form (age at neurologic onset)	Typical picture
Perinatal (systemic)	Fetal ascites, prolonged cholestatic jaundice, hepatosplenomegaly, lung infiltrates; fatal liver or multiorgan failure within 6 months in 3 to 12% of all cases
Early infantile (under 2 years)	Hypotonia and delayed motor milestones; hepatosplenomegaly or prolonged neonatal jaundice almost always
Late infantile (2 to 6 years)	Clumsiness, gait problems, speech delay; gaze palsy often missed; cataplexy or hearing loss can come first
Juvenile (6 to 15 years)	Falling school performance, ataxia, dystonia, vertical supranuclear gaze palsy
Adolescent and adult (over 15 years)	Psychosis, depression or bipolar-like illness, early dementia, ataxia; splenomegaly often absent

The earlier the neurologic onset, the faster NPC progresses.

Diagnosis: enzyme, genes, biomarkers

ASMD:

Enzyme assay (required): acid sphingomyelinase activity in leukocytes or cultured fibroblasts, usually below 10% of controls. Dried blood spot results must be confirmed, and residual activity does not predict the subtype.
Genetics: the diagnosis rests on biallelic SMPD1 pathogenic variants plus low enzyme activity.
Biomarkers: lyso-sphingomyelin is the most specific, rising markedly only in ASMD; it is best combined with PPCS (formerly lyso-sphingomyelin-509), which is high in both ASMD and NPC. Chitotriosidase rises only modestly and is nonspecific.

NPC:

First line: plasma biomarkers (oxysterols such as cholestane-3β,5α,6β-triol, PPCS and bile acid derivatives) plus NPC1/NPC2 genetic testing, usually by exome sequencing or a multigene panel. Lyso-sphingomyelin is only slightly raised in NPC, which helps separate it from ASMD.
Filipin test (cultured fibroblasts stained for unesterified cholesterol) is no longer first line; it is kept for inconclusive results and new variants.

Treatment: FDA-approved drugs and their exact label scope

Drug (brand), FDA approval	US label indication	Label points to know
Olipudase alfa (Xenpozyme), Aug 2022	Non-central nervous system manifestations of ASMD in adults and children	IV every 2 weeks; dose escalation to 3 mg/kg limits infusion reactions and transaminase rises; boxed warning for hypersensitivity, including anaphylaxis; not expected to cross the blood-brain barrier
Arimoclomol (Miplyffa), Sep 2024	With miglustat, neurological manifestations of NPC, age 2 years and older	Oral, three times daily by weight; urticaria and angioedema; embryofetal toxicity; raises creatinine 10 to 20% without changing glomerular function
Levacetylleucine (Aqneursa), Sep 2024	Neurological manifestations of NPC, weight 15 kg or more; since September 2026 also ataxia in ataxia-telangiectasia	Oral granules for suspension, two or three doses daily by weight; no partner drug required; embryo-fetal toxicity, so confirm pregnancy status first
Miglustat (Zavesca and generics), 2003	Adults with mild to moderate type 1 Gaucher disease when enzyme replacement is not an option; as Opfolda, with cipaglucosidase alfa for some adults with late-onset Pompe disease	No US label indication for NPC; approved for NPC in the EU, Canada and Japan; in US NPC care it is arimoclomol's required partner

Limits: olipudase alfa improves the spleen, liver, lungs, platelets, lipids and growth but not type A brain disease.
Supportive care: in ASMD, avoid total splenectomy, which worsens lung disease; in NPC, cataplexy can respond to tricyclics such as protriptyline or to modafinil.

USMLE traps: classic teaching vs current evidence

Trap	What's actually true
Every Niemann-Pick type is a sphingomyelinase deficiency	Only types A, A/B and B; type C is an NPC1/NPC2 cholesterol-transport defect
Cherry-red spot plus regression means Tay-Sachs	Check the abdomen: hepatosplenomegaly points to Niemann-Pick A (or Sandhoff, GM1)
Foam cells prove Niemann-Pick A/B	Also NPC, acid lipase deficiency, GM1, Tangier and atherosclerotic plaque; confirm biochemically and genetically
No organomegaly rules out NPC	Many NPC patients never have it
Filipin staining is the test for NPC	Biomarkers plus NPC1/NPC2 genetics come first
Olipudase alfa treats Niemann-Pick	Only non-CNS manifestations of ASMD; not type A brain disease, not NPC
Cataplexy means narcolepsy	With ataxia, vertical gaze palsy and a neonatal jaundice history, think NPC (narcolepsy type 1 is loss of orexin neurons)
NPC1L1 is NPC1	Ezetimibe blocks NPC1L1, the intestinal brush-border sterol transporter

More biochemistry walkthroughs are on the Biochemistry hub.

Worked USMLE-style vignettes

Vignette 1: the infant with a big abdomen. A 10-month-old girl of Ashkenazi Jewish descent has had hepatosplenomegaly since 3 months and poor weight gain. She sat at 7 months but no longer can, and she has had three respiratory infections with interstitial infiltrates on chest x-ray. Funduscopy shows cherry-red spots; marrow shows large macrophages with foamy cytoplasm. Which enzyme is deficient? (A) Acid α-glucosidase (B) Acid sphingomyelinase (C) Galactocerebrosidase (D) Glucocerebrosidase (E) Hexosaminidase A (F) N-acetylglucosamine-1-phosphotransferase

Answer: B, infantile neurovisceral ASMD (type A).

A (Pompe disease): glycogen, not lipid; hypertrophic cardiomyopathy in the first weeks (see the Pompe disease mnemonic).
C (Krabbe disease): extreme irritability and rapid decline from a leukodystrophy, with high psychosine.
D (Gaucher disease): wrinkled-paper storage cells; interstitial lung disease this early favors ASMD.
E (Tay-Sachs disease): the cherry-red spot and regression fit, but the liver and spleen stay normal-sized.
F (I-cell disease): skeletal deformities from birth, coarse facies, gingival hypertrophy; enzymes are secreted instead of reaching lysosomes.

Vignette 2: the adult with splenomegaly and dyspnea. A 32-year-old man has splenomegaly, platelets of 92,000/mm3, exertional dyspnea with interstitial changes on CT, HDL of 21 mg/dL and a normal neurologic examination. Marrow shows foamy histiocytes and a few with blue-green granules. Leukocyte acid sphingomyelinase activity is 4% of control, with two pathogenic SMPD1 variants. Which disease-specific treatment is most appropriate? (A) Arimoclomol with miglustat (B) Imiglucerase (C) Miglustat alone (D) Olipudase alfa (E) Total splenectomy

Answer: D. This is chronic visceral ASMD (type B), and olipudase alfa is labeled for its non-CNS manifestations.

A: labeled for the neurological manifestations of NPC.
B: Gaucher enzyme replacement; wrong enzyme.
C: US miglustat labels cover type 1 Gaucher disease, not ASMD.
E: total splenectomy is avoided in ASMD because it worsens lung disease.

Vignette 3: the boy who drops when he laughs. An 11-year-old boy has falling grades, clumsiness and frequent falls. Asked to look down, he blinks and drops his head instead of moving his eyes; horizontal gaze is normal. Several times he has gone limp while laughing, without losing consciousness. He had prolonged neonatal jaundice, and the spleen tip is palpable. What is the underlying defect? (A) Acid sphingomyelinase deficiency (B) ATP7B copper transporter deficiency (C) Defective lysosomal export of LDL-derived cholesterol (D) Hexosaminidase A deficiency (E) Loss of hypothalamic orexin (hypocretin) neurons

Answer: C, NPC, usually from NPC1 variants. Test plasma biomarkers with NPC1/NPC2 sequencing; US options are arimoclomol with miglustat, or levacetylleucine.

A: type B ASMD lacks progressive brain disease; gaze palsy with gelastic cataplexy is the NPC signature.
B (Wilson disease): mixes liver, movement and psychiatric problems; look for low ceruloplasmin and Kayser-Fleischer rings.
D (juvenile Tay-Sachs): gait problems and regression, but liver and spleen involvement is not typical.
E (narcolepsy type 1): cataplexy comes with excessive daytime sleepiness and hypnagogic hallucinations, not ataxia or gaze palsy.

Vignette 4: the startled baby with a flat abdomen. A 7-month-old boy of Ashkenazi Jewish descent has been losing head control since age 5 months and flings out his arms at every loud noise. Funduscopy shows bilateral cherry-red spots; the liver and spleen are not palpable, and the lungs are clear. Which enzyme is deficient? (A) Acid sphingomyelinase (B) β-Galactosidase (C) Glucocerebrosidase (D) Hexosaminidase A (E) Hexosaminidase A and B

Answer: D, infantile Tay-Sachs disease (HEXA, GM2 ganglioside).

A (Niemann-Pick type A): hepatosplenomegaly by about 3 months, lung disease and foam cells.
B (GM1 gangliosidosis): cherry-red spot plus hepatosplenomegaly, coarse facies and skeletal disease.
C (Gaucher type 2): hepatosplenomegaly with hypertonia and opisthotonos.
E (Sandhoff disease): the Tay-Sachs course plus hepatomegaly and bone changes, with no ethnic association.

Key takeaways

FOAMY = ASMD (types A, A/B, B): foam cells, organomegaly, acid sphingomyelinase (SMPD1), macular cherry-red spot, young death in type A.
Foam cells are lipid-laden macrophages in marrow, spleen, liver and lungs, sometimes with sea-blue histiocytes; neither is specific, and Gaucher cells look like wrinkled paper.
Tay-Sachs vs Niemann-Pick: both have a cherry-red spot; only Niemann-Pick A has hepatosplenomegaly.
NPC is a separate disease: NPC1/NPC2 cholesterol export; vertical supranuclear gaze palsy, gelastic cataplexy, ataxia; diagnose with biomarkers plus genetics.
US labels: olipudase alfa for non-CNS ASMD; arimoclomol with miglustat (age 2 and older) or levacetylleucine (15 kg or more) for neurologic NPC; miglustat alone is not FDA-approved for NPC.