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[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# Sphingomyelin

Sphingomyelin is the sphingolipid with phosphate: rich in myelin and the outer leaflet of membranes. It builds up in Niemann–Pick disease.

Updated 2026-11-01

Loading the 3D model…

## Key facts

- Ceramide + phosphocholine; it is both a sphingolipid and a phospholipid.
- It is made in the Golgi: sphingomyelin synthase moves phosphocholine from phosphatidylcholine to ceramide.
- Lysosomal acid sphingomyelinase breaks it into ceramide + phosphocholine; its deficiency causes Niemann–Pick A and B.
- With cholesterol it forms the lipid rafts of the outer leaflet.

**Also called**
N-stearoyl sphingomyelin (3D model)

**Formula**
C₄₁H₈₃N₂O₆P

**PubChem**
[CID 6453725](https://pubchem.ncbi.nlm.nih.gov/compound/6453725)

## Structure

- The 3D model (PDB A1H8M) is C18 sphingomyelin: sphingosine + stearate + phosphocholine.
- The same phosphocholine head as lecithin, but on a sphingosine backbone instead of glycerol.

## Clinical notes

- In Niemann–Pick A/B it accumulates in macrophages (foam cells) of liver, spleen, lung and bone marrow.
- An amniotic fluid lecithin/sphingomyelin ratio above 2 indicates mature fetal lungs.

## Related conditions

- [Niemann–Pick disease](https://durgical.com/en/conditions/niemann-pick-disease/)

## Related

- [Ceramide](https://durgical.com/en/biochemistry/molecules/ceramide/)
- [Acid sphingomyelinase](https://durgical.com/en/biochemistry/enzymes/acid-sphingomyelinase/)
- [Phosphatidylcholine (lecithin)](https://durgical.com/en/biochemistry/molecules/phosphatidylcholine/)
- [Sphingolipids and sphingolipidoses](https://durgical.com/en/biochemistry/topics/sphingolipids-and-sphingolipidoses/)
- [Membrane structure](https://durgical.com/en/biochemistry/topics/membrane-structure/)
- [Phospholipids](https://durgical.com/en/biochemistry/topics/phospholipids/)

## Test yourself

Think of the answer, then tap the question to see it.

## How does sphingomyelin differ chemically from phosphatidylcholine?

Both carry phosphocholine, but sphingomyelin is built on ceramide (sphingosine) and lecithin on glycerol.

## Which enzyme breaks down sphingomyelin in the lysosome?

Acid sphingomyelinase (SMPD1 gene), which splits it into ceramide and phosphocholine.

## What does an amniotic lecithin/sphingomyelin ratio above 2 indicate?

Enough surfactant: the fetal lungs are mature.

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Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [N-Stearoylsphingomyelin (CID 6453725)](https://pubchem.ncbi.nlm.nih.gov/compound/6453725) (PubChem, NCBI, 2026) · Public domain; [RCSB PDB - A1H8M Ligand Summary Page](https://www.rcsb.org/ligand/A1H8M) (RCSB Protein Data Bank, 2026); [Sphingolipid metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-428157) (Reactome, 2026); [SMPD1 gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/smpd1/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.

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