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Niemann-Pick: when sphingomyelin will not go away
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Biochem · Lysosomal Storage Disease

Niemann-Pick: when sphingomyelin will not go away

Sphingomyelinase is broken. Sphingomyelin piles up inside macrophage lysosomes. The liver and spleen blow up, the marrow fills with foam cells, the macula still goes cherry red. Every clue in one walk.

AR · SMPD1 gene Foam cells in marrow Cherry-red macula
Pick your liver with your foam sphinger

The Case

Nine months old. The belly grew first.

Read the story, commit to your answer, then tap to see what the marrow says.

Vignette · Inpatient peds

A 9-month-old infant is admitted for failure to thrive and developmental regression. He met milestones until about 4 months, then stopped sitting, then stopped tracking faces. His parents noticed his abdomen grew before the regression did · clothes that fit at 6 months no longer button. On exam he is hypotonic, the liver is palpable 6 cm below the costal margin, the spleen is palpable 5 cm below the costal margin. Fundoscopy shows a pale macula with a deep red foveal center. Bone marrow biopsy is sent.

Niemann-Pick disease, type A The anchor: infant + huge liver and spleen + cherry-red macula + foam cells on marrow. The detail that closes Tay-Sachs out: the belly. Tay-Sachs keeps a soft abdomen because storage is inside neurons. Niemann-Pick stores sphingomyelin inside macrophages, and macrophages live in liver, spleen, lymph nodes, and marrow · so those organs swell. Foam cells = lipid-laden macrophages with a vacuolated, foamy cytoplasm. The cherry-red comes free because retinal ganglion cells around the fovea also load with sphingomyelin and turn pale.

The Four Clues

Four flags that anchor Niemann-Pick

Each one alone could be something else. Together they only fit one disease.

Clue 01

Sphingomyelinase missing

The lysosome owns a scissor enzyme called acid sphingomyelinase (SMPD1 gene). Its job is to cut sphingomyelin into ceramide plus phosphocholine. In types A and B the scissor is broken. Enzyme assay shows near-zero activity in white blood cells or cultured fibroblasts.

Clue 02

Huge liver and spleen

Sphingomyelin stacks inside macrophage lysosomes. Macrophages live in the liver (Kupffer cells), spleen (red pulp), lymph nodes, and bone marrow. Those organs swell as the loaded cells pile up. HSM is the line between Niemann-Pick and Tay-Sachs.

Clue 03

Cherry-red macula

Retinal ganglion cells around the fovea load with sphingomyelin and turn pale white. The fovea has no ganglion cells, so it stays red against the pale ring. Same fundus picture as Tay-Sachs and Sandhoff. The eye alone cannot tell them apart.

Clue 04

Foam cells in bone marrow

Foam cell = macrophage stuffed with sphingomyelin until its cytoplasm looks like soap bubbles under the microscope. Marrow biopsy or splenic aspirate shows sheets of them. This is the histology giveaway and the second line that separates Niemann-Pick from Tay-Sachs.

Anchor It

Memory hooks

Tap each line to reveal the hook. These are the sentences that stick on test day.

Board Hooks
Cherry-red macula + hepatosplenomegaly + foam cells = Niemann-Pick A. Cherry-red macula + NO hepatosplenomegaly = Tay-Sachs.
Sphingomyelinase cuts sphingomyelin into ceramide + phosphocholine. No scissors = sphingomyelin stacks in lysosomes = foam cells.
Type C is the oddball: normal sphingomyelinase, broken NPC1/NPC2 cholesterol transporter. Vertical gaze palsy + ataxia + HSM.
Foam cell = soap-bubble cytoplasm (small clear vacuoles). Gaucher cell = wrinkled tissue-paper (crumpled fibrillar sheets).
Olipudase alfa (ERT) works for type B visceral disease. Cannot cross BBB, so useless for type A neurodegeneration.

The Mechanism

The macrophage with the scissor missing

Toggle the enzyme on and off. Watch sphingomyelin either get cut to ceramide or stack up until the macrophage bloats into a foam cell.

LYSOSOME ASMase SPHINGOMYELIN CERAMIDE FOAM VACUOLES MACROPHAGE SWELLS
Healthy Acid sphingomyelinase cuts sphingomyelin into ceramide plus phosphocholine. The lysosome stays compact, the macrophage stays its normal size, the liver and spleen stay normal.

The Eye Finding

Both diseases give the same cherry-red macula

Schematic fundus on the left for Niemann-Pick, on the right for Tay-Sachs. The eye alone cannot break the tie · the belly does.

Niemann-Pick A Sphingomyelin in ganglion cells
Tay-Sachs GM2 ganglioside in ganglion cells
Same picture, different storage Around the fovea, retinal ganglion cells swell with stored lipid and turn pale white-yellow. The fovea itself has no ganglion cells, so the choroidal red shows through. Niemann-Pick stores sphingomyelin in those ganglion cells. Tay-Sachs stores GM2 ganglioside. Same look, two different shipments. The next move is: see cherry-red, then go palpate the belly. Soft belly = Tay-Sachs. Huge liver and spleen = Niemann-Pick.

The Tiebreaker

Niemann-Pick vs Tay-Sachs side by side

Same fundus, two diseases. The belly, the head, the marrow, the ear · every line draws the same direction.

 
Niemann-Pick A
Tay-Sachs
Enzyme
Sphingomyelinase (SMPD1)
Hexosaminidase A (HEXA)
Substrate
Sphingomyelin
GM2 ganglioside
Storage cell
Macrophages
Neurons
Belly
Huge HSM
NO HSM
Marrow
Foam cells
Clean
Head
Variable / normal
Macrocephaly
Ear
Not a feature
Hyperacusis
Macula
Cherry-red · shared finding
Cherry-red · shared finding
Survival
Death by 2-3 yr (type A)
Death by 3-5 yr
Board shortcut Cherry-red macula in an infant. Feel the belly. Huge liver and spleen plus foam cells in marrow = Niemann-Pick A. Soft belly with macrocephaly and an exaggerated startle = Tay-Sachs. If the picture is an older child with vertical gaze palsy plus ataxia plus HSM, jump to Niemann-Pick C · same family name, different gene (NPC1 / NPC2), different mechanism (cholesterol trafficking).

The Three Variants

Three Picks, three different patients

Same family name, three different stories. Types A and B share the broken sphingomyelinase. Type C is its own animal · a cholesterol traffic jam.

A
Severe infantile
SMPD1 · sphingomyelinase out
  • Onset: 3-6 months
  • Neuro: rapid regression, hypotonia
  • Belly: massive HSM
  • Eye: cherry-red macula
  • Marrow: foam cells
  • Death: age 2-3
Severe · visceral + brain
Why type C is the trap Same family name, completely different mechanism. Type C is not a sphingomyelinase problem · it is a cholesterol traffic jam. NPC1 and NPC2 proteins normally move cholesterol out of the late endosome / lysosome. When they fail, cholesterol piles up and so does some sphingomyelin secondarily, but the enzyme assay reads normal. The board key is the eye movement: vertical supranuclear gaze palsy in a kid or teen with HSM and falls. Treatment is miglustat (substrate reduction) · supportive otherwise.

Clinical Photos

What it looks like

Foam cells, cherry-red macula, and organ involvement. Tap any image for full view.

Cherry-red macula on fundoscopy in storage disease Cherry-red macula: pale ganglion ring around red fovea
Cherry red spot on fundoscopic examination Cherry-red spot: classic fundoscopic finding in NPA and Tay-Sachs
Infant with hepatosplenomegaly showing abdominal distension Hepatosplenomegaly: distended abdomen in infant with storage disease

clinical Walkthrough

25 original vignettes, shuffled

One at a time. Cover the choices, hunt the stem clue, answer bottom up. Right-click or long-press to cross out. Double-click or double-tap to highlight.

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End of Deep-Dive

Sphingomyelinase missing → sphingomyelin stacks in macrophages → liver and spleen blow up → marrow fills with foam cells → macula still goes cherry red. Pick your liver with your foam sphinger.

Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last updated July 1, 2026 at 10:03 PM ET
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