ABCG2 Genotype

Two people take the same dose of rosuvastatin. One ends up with roughly twice as much drug circulating in the blood as the other, and a higher chance of muscle aches bad enough to quit the prescription. A single inherited letter change in one gene explains a lot of that gap.

That same letter change is one of the strongest known genetic drivers of gout. Reading this gene answers two questions at once: how well your body gets rid of uric acid, and how hard a handful of common drugs hit you at a standard dose.

The Pump This Gene Builds

The gene's formal name is ATP-binding cassette sub-family G member 2. It carries the instructions for a pump that sits on the outward-facing surface of cells and pushes unwanted molecules out. Two copies of the protein lock together to form one working pump, and each pump burns cellular fuel to shove its cargo across the membrane. Uric acid is one of its main natural cargoes. Dozens of drugs are the rest.

The pump is densest where your body does its exporting: the kidney tubules that make urine, the lining of the small intestine, and the bile ducts draining the liver. It also guards borders, sitting in the placenta and in the blood vessels of the brain, where it keeps circulating compounds from crossing in.

The protein has a confusing name. It's called breast cancer resistance protein, or BCRP, because researchers first found it in breast cancer cells that were shrugging off chemotherapy. The name says where it was discovered. It says nothing about your breast cancer risk.

Gout and High Uric Acid

The useful thing this genotype tells you isn't just whether your uric acid runs high. It's whether high uric acid is likely to turn into actual gout. In a study of roughly 17,700 people, the common reduced-function variant was tied to the step where high uric acid progresses to a diagnosed attack, not only to the urate number itself. Plenty of people walk around with elevated urate and never get gout. This is part of what separates them.

The mechanism is not what most people assume. Human studies of carriers showed the variant mainly cripples urate disposal through the gut, not the kidney. Your intestine is a real urate exit route, and this pump is a big part of it. Block it and urate backs up even when your kidneys are working fine.

Sources: PAGE Study (Zhang et al.); Higashino et al.; Wrigley et al.

What this means for you: if gout showed up early in your family, or showed up in relatives who eat and drink sensibly, the explanation may be structural rather than dietary. Rare null variants that wipe out the pump entirely have been traced through families with gout starting in childhood and adolescence. Sequencing the whole gene, rather than checking one common spot, is what finds those.

The picture is not identical across ancestries. In Han Chinese men, two variants raised gout risk while a third appeared protective, and the common risk variant is far more frequent across East Asian populations than European ones. Alcohol intake and male sex stack on top of the genotype rather than washing it out.

Kidney Stones

Urate that can't leave has to go somewhere. In a Taiwanese biobank study of about 120,000 adults, people with one or two copies of the common reduced-function allele had about 12% to 18% higher odds of kidney stones after accounting for other factors. Regular exercise was linked to lower stone risk in the same dataset.

A separate case-control study of about 35,000 people found that a second variant in this gene and one in a different urate transporter added to gout risk. For kidney stones, the signal was weaker: the variant in this gene showed a modest independent link, while the other transporter variant did not clearly add stone risk. So a reduced-function result isn't the whole urate story, and it reads differently alongside other transporter variants.

Statins, Muscle Symptoms, and Quitting the Drug

This is the part with the clearest day-to-day payoff. In controlled human drug-level work, people with two copies of the common variant had about 144% higher rosuvastatin exposure and about 72% higher atorvastatin exposure than people without it. That is not a rounding error. It's the difference between a starting dose and an effectively doubled one.

More drug does two things at once. Carriers tend to get more LDL lowering from the same milligrams, and they may carry more risk of muscle symptoms. In a multiethnic cohort of 422 people on rosuvastatin, those with two copies of the reduced-function allele had the highest risk of stopping the drug, and carriers were more common among discontinuers than continuers. CPIC statin guidance recommends lower rosuvastatin doses for poor-function ABCG2 phenotypes.

If you've already abandoned a statin because it made your legs ache, this genotype is worth knowing before you conclude that statins aren't for you. A reduced-function result reframes the problem as a dosing problem rather than a drug-class problem.

When Allopurinol Underperforms

The Dutch Pharmacogenetics Working Group, a body that writes gene-drug dosing guidance used across European practice, has a formal recommendation here. Carriers of the common variant respond poorly to standard allopurinol doses and may need a higher dose target or a different urate-lowering drug. A replication study and meta-analysis confirmed the poor-response association, and a genome-wide study of about 4,400 people treated with allopurinol found the same variant shaping response.

There's a second, quieter implication. Reduced pump function may also make some urate-excretion strategies less predictable, especially drugs meant to increase urate exit. So the genotype doesn't point to one easy substitute. It says to check the response early, then adjust the dose or the agent instead of assuming the first plan worked.

Cancer Drugs and Other Substrates

The same reduced efflux shows up across oncology drugs, and the direction of benefit flips depending on the drug. Carriers of the common variant had higher trough levels of imatinib in a pooled analysis, and women with advanced ovarian cancer who carried it lived longer without progression on platinum and taxane chemotherapy. More drug staying inside cells is sometimes exactly what you want.

It cuts the other way too. A meta-analysis found the common variant predicted low platelet counts and hand-foot syndrome with sunitinib in Asian populations. In a cohort of 100 Chinese people with advanced lung cancer on targeted tyrosine kinase inhibitor drugs, a different variant in this gene was tied to shorter overall survival.

The counterweight is simple. The effect isn't universal across drugs. The common variant had little influence on irinotecan handling in European populations, and a study of 385 people on rivaroxaban found no link between these variants and clinically relevant bleeding. Reviews of the whole transporter family conclude that any single variant often has modest impact on drug availability, because how much pump your cells actually make is also shaped by things your DNA sequence doesn't capture.

A Heart Finding That Runs the Other Way

Here is a result that looks backwards. In a Taiwanese study of about 139,000 adults, people carrying two copies of the reduced-function variant had lower calculated cardiovascular risk scores, with the effect clearest in non-obese women who also had high urate, where the odds of a higher risk score were roughly 24% lower. Higher urate, lower heart risk score. That shouldn't happen if urate is simply bad.

The resolution is that urate is not one thing. In the general population, high urate usually travels with obesity, insulin resistance, and heavy drinking, and those companions carry most of the cardiovascular risk. This variant raises urate a different way, by blocking an exit door, so the number climbs without the metabolic baggage behind it. Read your result as information about how you clear urate and drugs, not as a heart risk score in either direction.

Carrying the Variant Is Not the Same as Getting Sick

Most carriers never develop the problems on this page. A biobank analysis of 486,956 people found that the extra risk of drug-related adverse events among carriers of pharmacogenetic risk variants, this gene included, was small in absolute terms, and the large majority of carriers had no such event. The common variant is too frequent, especially across East Asian ancestries, to be treated as a diagnosis.

What a reduced-function result actually buys you is a shifted prior. It tells you which explanations to reach for first when your urate won't come down, when a standard statin dose produces outsized symptoms, or when gout shows up decades earlier than it should.

A Result You Only Need Once

This is a sequence you were born with. It will read the same at 40 as it did at 20, so there's no trend to track and no reason to repeat the test. The only situation that justifies running it again is doubt about the call itself, which is a different problem and is handled by confirming the specific variant with a second method.

The things worth tracking are the downstream numbers. If you carry a reduced-function result, get serum uric acid and kidney function, ideally both creatinine-based and cystatin C-based estimates, at least once a year rather than waiting for a symptom. If you're on a statin or starting one, recheck your lipids within a couple of months of any dose change and say something the first time your muscles feel off rather than at the annual visit.

That yearly cadence is the floor, not the target. If you're actively working on urate, whether through medication or diet, checking every three to six months tells you whether the strategy is working while you can still change it.

What to Do With a Reduced-Function Result

Order the companion tests that turn a genotype into a decision. Serum uric acid and kidney function tell you whether the transport problem has produced anything measurable yet. An SLCO1B1 genotype helps interpret statin handling, and HLA-B*58:01 is the safety genotype often checked before allopurinol. If you're on a statin and have muscle symptoms, add creatine kinase, a blood marker of muscle breakdown.

Then read the combinations. Reduced function plus high urate plus a family history of early gout means you should expect standard allopurinol dosing to fall short and plan for a higher dose target or a different agent from the start. Reduced function plus statin muscle symptoms means the symptoms are more likely a real exposure problem than coincidence, which argues for a dose change rather than abandoning the class. Reduced function with normal urate and no relevant prescriptions means you file the result and act on it later.

Bring in help for two specific situations. Gout that won't respond to treatment is a rheumatology question. A rare or uncertain variant is a genetic counseling question, and that one matters more than it sounds: in a randomized trial, clinicians without genetics training made clinically significant errors when disclosing sequencing results, while genetic counselors did not.

Where This Result Can Mislead You

• Genotype is not current pump activity: the sequence tells you what your cells are instructed to build, not how much working pump they have today. Other regulatory factors also change pump levels, which is one reason single variants predict drug levels better than they predict outcomes.
• Ancestry changes what the result means: the common variant is much more frequent in East Asian populations than in European ones, and risk estimates from one population don't transfer cleanly to another. Interpret your result against the population you descend from.
• A normal result only rules out what was tested: some panels check only common spots. Even broader sequencing can miss changes buried outside the usual gene-reading zones or larger rearrangements.
• Rare variants often arrive with a shrug: sequencing turns up rare changes whose effect on the pump nobody has measured. Laboratory work on rare variants from gout cohorts found some abolish transport entirely and others don't, and classification still differs between labs, so an unfamiliar variant may be reported as uncertain rather than good or bad.
• The sample has to reflect the DNA you were born with: buccal, saliva, and blood usually give the same inherited call, but a bone marrow transplant, some blood cancers, or a poor swab can make the sample less straightforward. If the result doesn't fit the family pattern, confirm the variant with a second method.
• Consumer raw data is not the same as a clinical report: direct-to-consumer files can miss rare variants, rely on imputation, or label a single spot without confirmation. Use a clinical-grade result for dosing, family, or treatment decisions.