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# MicroRNA, RNA interference and antisense drugs

Short RNAs can switch off a gene after it has been copied into mRNA; cells use them naturally, and medicine now uses them as drugs.

Updated Nov 12, 2026

## Key facts

- MicroRNAs (miRNAs) are made by the cell and are about 22 nucleotides long; each pairs partly with many mRNAs and lowers their translation or stability.
- Small interfering RNAs (siRNAs) pair exactly with one mRNA; loaded into the RISC complex, they guide it to cut that mRNA.
- Antisense oligonucleotides are short, chemically modified single strands that bind a target RNA and cause its breakdown or change its splicing.
- These drugs lower or correct a protein without changing the DNA.

## In detail

- miRNA genes are transcribed, trimmed by Drosha in the nucleus and by Dicer in the cytoplasm, and then work inside RISC.
- One miRNA can tune hundreds of genes; miRNA levels are altered in many cancers.
- Getting the drug to its tissue is the main problem: liver-targeted siRNAs are often linked to GalNAc, a sugar that liver cells take up.
- Splice-switching antisense drugs can make the cell skip an exon (some Duchenne treatments) or keep one (nusinersen in spinal muscular atrophy).

**Also called**
miRNA and siRNA, RNA silencing

## Clinical notes

- Inclisiran, an siRNA against PCSK9, lowers LDL cholesterol.
- siRNA and antisense drugs that lower transthyretin are used in hereditary transthyretin amyloidosis.
- Lumasiran, an siRNA, reduces oxalate production in primary hyperoxaluria type 1.
- Nusinersen changes SMN2 splicing so that more working SMN protein is made.

## Test yourself

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

## How does an siRNA differ from a microRNA?

An siRNA pairs exactly with one mRNA and leads to its cleavage; a microRNA pairs partly with many mRNAs and mainly dampens their translation.

## How does nusinersen help in spinal muscular atrophy?

It is an antisense drug that changes SMN2 splicing so exon 7 is kept and more working SMN protein is made.

## Why are many siRNA drugs linked to GalNAc?

Liver cells take up GalNAc, so the drug reaches the liver, where its target protein is made.

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## Connections

## Related conditions 4

- [Spinal muscular atrophy](https://durgical.com/en/conditions/spinal-muscular-atrophy/)
- [Duchenne muscular dystrophy](https://durgical.com/en/conditions/duchenne-muscular-dystrophy/)
- [Primary hyperoxaluria](https://durgical.com/en/conditions/primary-hyperoxaluria/)
- [Familial hypercholesterolemia](https://durgical.com/en/conditions/familial-hypercholesterolemia/)

## Related 8

- [RNA processing (cap, poly-A tail and splicing)](https://durgical.com/en/biochemistry/topics/rna-processing/)
- [Spliceosome](https://durgical.com/en/biochemistry/enzymes/spliceosome/)
- [Translation and the genetic code](https://durgical.com/en/biochemistry/topics/translation-and-the-genetic-code/)
- [PCSK9](https://durgical.com/en/biochemistry/enzymes/pcsk9/)
- [Transthyretin (prealbumin)](https://durgical.com/en/biochemistry/enzymes/transthyretin/)
- [Gene therapy](https://durgical.com/en/biochemistry/topics/gene-therapy/)
- [Control of gene expression in human cells](https://durgical.com/en/biochemistry/topics/control-of-gene-expression-in-human-cells/)
- [Central dogma of molecular biology](https://durgical.com/en/biochemistry/topics/central-dogma-of-molecular-biology/)

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

Sources: [Antisense](https://www.genome.gov/genetics-glossary/Antisense) (National Human Genome Research Institute (NHGRI), 2026); [Gene Expression](https://www.genome.gov/genetics-glossary/Gene-Expression) (National Human Genome Research Institute (NHGRI), 2026); [What is gene therapy?: MedlinePlus Genetics](https://medlineplus.gov/genetics/understanding/therapy/genetherapy/) (MedlinePlus, US National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/microrna-rna-interference-and-antisense-drugs/