Statin Gene Testing: SLCO1B1 Explained

Pharmacogenomics studies how your genes change the way a medicine works in your body. For statins, three genes have formal guideline advice: SLCO1B1 (all statins), ABCG2 (rosuvastatin) and CYP2C9 (fluvastatin).

Two expert groups turned the evidence into prescribing advice. CPIC, a US-based group, published its statin guideline in 2022. The Dutch DPWG published its SLCO1B1 guideline in 2024.

SLCO1B1 makes a transporter (OATP1B1) on liver cells that pulls statins out of the blood and into the liver. When it works less well, more statin stays in the blood and reaches muscle. The key variant is c.521T>C, found in the *5 and *15 versions of the gene.

The variant is common. In the DPWG review, the C version appeared in about 14 to 22% of gene copies in people of European ancestry, 8 to 16% in East Asian populations and about 11% in Latin American populations.

A genome-wide study of people taking simvastatin 80 mg a day found that each copy of the C version raised the odds of myopathy about 4.5 times, and two copies about 17 times. More than 60% of myopathy cases in that study traced to the variant.

For reduced SLCO1B1 function, CPIC says to choose a different statin instead of simvastatin. If simvastatin is truly needed, keep it under 20 mg a day for poor function. For atorvastatin, CPIC suggests starting at 40 mg or less (decreased function) or 20 mg or less (poor function), and adding a non-statin medicine if more lowering is needed.

A common ABCG2 variant (c.421C>A) lowers working transporter by about 30 to 40%. People with two copies had about 144% higher rosuvastatin levels than people with none. For poor ABCG2 function, CPIC advises starting rosuvastatin at 20 mg or less. CPIC notes the actual myopathy risk for this group is unknown.

CYP2C9 breaks down fluvastatin. CPIC advises starting at 40 mg a day or less for intermediate metabolizers and 20 mg a day or less for poor metabolizers. This result rarely changes a plan, because doctors do not prescribe fluvastatin often.

No. CPIC says to avoid stopping a needed statin because of a gene result. The usual response is a different statin or a lower dose, often with ezetimibe added. Ask your clinician before you change anything.

If you have taken your statin without muscle problems, CPIC considers it reasonable to continue: at least 4 weeks for a moderate-risk result, at least a year for a high-risk result. CPIC says these time frames rest mostly on expert opinion.

DPWG rates testing as essential before simvastatin 80 mg a day, beneficial before lower simvastatin doses, and potentially beneficial before atorvastatin or rosuvastatin. Testing most often changes a plan for people about to start simvastatin, people with muscle symptoms on two or more statins, and people who take several interacting medicines.

No trial yet proves gene-guided prescribing prevents muscle problems. Most people with a variant take statins without trouble. A test can miss rare variants, and a gene result cannot tell you whether a past ache came from a statin. Dose, drug interactions, age, thyroid function and kidney or liver disease often raise muscle risk more than genes do.