Simvastatin: the statin most affected by one transporter gene
Of the seven statins with published pharmacogenomic guidance, simvastatin is the one where the genetics bite hardest. If you stopped a statin because of muscle aches, there is a reasonable chance it was this one.
Also sold as: Zocor, Simvastatin Teva.
What simvastatin is
Simvastatin lowers LDL cholesterol by blocking an enzyme the liver uses to make it. It has been in wide use since the 1990s, it is cheap, and it works. Its main practical problem is muscle symptoms: aching, weakness or tenderness that leads a substantial number of people to stop taking it, occasionally with real muscle injury behind the complaint.
Why your genes come into it
A statin has to get into liver cells to do its job, and it does not drift in on its own. SLCO1B1 codes for a transporter that pulls statins out of the bloodstream into the liver. When that transporter works less well, the drug that should have been swept into the liver stays circulating instead, and higher levels in blood and muscle are where statin muscle symptoms come from. Simvastatin depends on this route more than the alternatives do, which is why its guidance is the most pointed of the seven and why the published advice at the low-function end is to consider a different statin rather than simply to lower the dose.
What published guidance says
The rows below restate CPIC's published guidance for each possible SLCO1B1 result. They describe a prescribing decision, not a self-service one. Stopping a statin carries its own cardiovascular risk, and a decreased-function result is a reason to have a conversation about which statin, not a reason to quit the class.
SLCO1B1
| If your SLCO1B1 result is | What that means | Published CPIC guidance |
|---|---|---|
| Decreased Function | Increased simvastatin acid exposure as compared to normal function; increased risk of myopathy | Per CPIC (A): "Prescribe an alternative statin depending on the desired potency (see Figure 1 of PMID: 35152405 for recommendations for alternative statins). If simvastatin therapy is warranted, limit dose to <20mg/day." |
| Increased Function | Typical myopathy risk and statin exposure | Per CPIC (A): "Prescribe desired starting dose and adjust doses based on disease-specific guidelines." |
| Normal Function | Typical myopathy risk and statin exposure | Per CPIC (A): "Prescribe desired starting dose and adjust doses based on disease-specific guidelines." |
| Poor Function | Increased simvastatin acid exposure compared to normal and decreased function; highly increased myopathy risk | Per CPIC (A): "Prescribe an alternative statin depending on the desired potency (see Figure 1 of PMID: 35152405 for recommendations for alternative statins)." |
| Possible Decreased Function | Increased simvastatin acid exposure as compared to normal function; increased risk of myopathy | Per CPIC (A): "Prescribe an alternative statin depending on the desired potency (see Figure 1 of PMID: 35152405 for recommendations for alternative statins). If simvastatin therapy is warranted, limit dose to <20mg/day." |
Can your DNA file answer this?
SLCO1B1 is one of the pharmacogenes a plain consumer file can genuinely answer, which makes this one of the better questions to bring to an old 23andMe or AncestryDNA export. The decreased-function *5 allele is tagged by a single position, rs4149056, that consumer arrays commonly carry, so Aimosti reads it from the standard report rather than only from aligned reads. Two limits: rarer SLCO1B1 alleles are not on the array, and if that position is missing from your file, the file cannot distinguish the reference allele from a position that was never read. The report says which of those it is instead of calling an unread position normal.
A genotyping chip reads only a few hundred thousand pre-selected positions, about 0.02% of your genome, chosen for common variation. It does not sequence the rest, so it cannot find the rare or novel pathogenic variants the clinical and carrier modules look for: a “no finding” from chip data means “this chip never looked”, far more so than with whole-genome sequencing. Chip data suits common-variant traits, pharmacogenomic tag SNPs, and haplogroup ancestry, not clinical or carrier screening.
Common questions
I get muscle aches on simvastatin. Will this explain them?
It might, and a decreased or poor function result gives a prescriber something concrete to work with. But statin muscle symptoms have causes unrelated to this gene, and a normal SLCO1B1 result does not mean the aches are imaginary. The value of the test is that it turns one plausible explanation into a checkable one.
If my result is decreased function, do I have to give up statins?
The published guidance for simvastatin at that end points toward a different statin chosen for the potency you need, or a capped simvastatin dose. It does not say avoid statins. The statins differ in how much they lean on this transporter, which is exactly why CPIC publishes a separate recommendation for each of the seven.
Which statin should I switch to?
That is a prescribing decision that weighs your cholesterol target, your cardiovascular risk and your other medications, not something a genotype alone settles. The CPIC guideline includes a figure comparing alternatives by potency, cited below, and it is the right document for your prescriber to look at rather than a substitution to make yourself.
Is SLCO1B1 in my 23andMe or AncestryDNA raw data?
Usually. It is one of the pharmacogenes where consumer chip data gives a real answer rather than a shrug, and Aimosti reads it from the file you already own. Where the position is missing or the genotype does not resolve, the result is reported as unresolved rather than assumed.