Your kidney stones keep returning. Your genes may explain why.

Your kidneys filter roughly 6,000 mg of phosphate per day. Under normal circumstances, the SLC34A1 protein reabsorbs about 80-90% of that phosphate back into your bloodstream so it isn’t wasted. The remaining phosphate exits in your urine to maintain balance.

SLC34A1 variants reduce the efficiency of this reabsorption process. Roughly 5-10% of the population carries a variant that impairs phosphate handling. When phosphate reabsorption fails, excess phosphate accumulates in your urine, where it combines with calcium to form calcium phosphate stones.

You might notice that your kidney stones seem to form despite low oxalate intake. Your blood chemistry looks normal. But your urine is saturated with phosphate because your kidneys aren’t reclaiming it efficiently. The stones form not from dietary oxalate but from this genetic inability to manage phosphate excretion.

Uromodulin is the most abundant protein in urine. It coats the inside of your kidney tubules and acts as a protective barrier, preventing calcium and other minerals from crystallizing and sticking together. It also helps defend against urinary tract infections by blocking bacterial adhesion.

UMOD variants reduce the amount of uromodulin your kidneys produce. Approximately 10-20% of people carry one or more variants affecting this gene. Lower uromodulin levels mean less protection against stone formation; minerals that should flow harmlessly through your urine are more likely to bind and crystallize.

You might form stones despite reasonable calcium and oxalate intake because you’re missing the protective coating that keeps minerals dissolved. Standard stone prevention doesn’t address this missing barrier. Your urine chemistry might look reasonable on a lab test, but the mechanical protection your kidney tubules need is simply absent.

Vitamin D doesn’t do anything by itself. It must bind to the VDR protein in your intestines and kidneys to activate calcium absorption and phosphate metabolism. Your VDR is essentially the lock into which vitamin D fits as the key.

VDR variants change the efficiency of this binding process and vitamin D signaling. Common variants affect how quickly and strongly your body responds to vitamin D. Some VDR variants reduce vitamin D signaling, which can impair the precise calcium-phosphate balance needed to prevent stone formation.

You might take vitamin D supplements and still have dysregulated calcium metabolism. Your body simply isn’t responding to vitamin D the way a person with a common VDR variant would. This means your calcium-phosphate balance remains unstable, favoring stone formation even when your dietary intake seems appropriate.

MTHFR converts dietary folate into methylfolate, the active form your cells can use. This reaction is crucial for one-carbon metabolism, which regulates amino acid processing. When one-carbon metabolism is impaired, homocysteine accumulates in your blood and urine.

MTHFR C677T variants, carried by roughly 30-40% of the population, reduce enzyme efficiency by 40-70%. Higher homocysteine levels increase urinary oxalate excretion and can directly promote calcium oxalate stone formation.

You might be forming stones because your body is producing more oxalate internally due to dysregulated amino acid metabolism, not because your diet is high in oxalate. Blood homocysteine might not be alarming by standard lab ranges, but it’s high enough to push you toward stone formation. Eating less spinach won’t address the underlying metabolic dysregulation.

AGXT is the enzyme responsible for breaking down oxalate that your body produces internally. Approximately 10% of your daily urinary oxalate comes from dietary sources; the other 90% comes from your body’s own metabolism of amino acids and other compounds. AGXT is the main pathway for disposing of that internally produced oxalate.

AGXT variants or loss-of-function mutations cause primary hyperoxaluria, a rare but severe genetic condition in which oxalate accumulates to dangerous levels. Carriers or those with mild variants still overproduce oxalate internally without necessarily meeting the threshold for primary hyperoxaluria diagnosis. Even if you eat almost zero dietary oxalate, your kidneys are flooded with internally produced oxalate that your deficient AGXT enzyme cannot break down.

You might have been diagnosed with idiopathic kidney stones despite maintaining an extremely low-oxalate diet. The reason is that your body is generating oxalate faster than your kidneys can excrete it. Dietary restriction becomes nearly pointless because the problem isn’t what you eat; it’s what your body produces.

Cystine is an amino acid that your kidneys filter and normally reabsorb almost completely. The SLC7A9 protein (along with SLC3A1) forms the transporter that pulls cystine back out of the filtrate so it doesn’t waste into urine. Without this transporter, cystine piles up in your urine.

SLC7A9 variants cause cystinuria, a rare genetic condition in which cystine cannot be reabsorbed. This results in extremely high urinary cystine levels. Cystine is poorly soluble at normal urine pH, so high concentrations form cystine stones that are notoriously difficult to dissolve and prone to recurrence.

If you have cystinuria, you’re not forming typical calcium oxalate stones. Your stones are made of cystine, and they behave very differently. Standard stone prevention fails completely because cystine stones require a completely different approach: aggressive hydration, urine alkalinization, and sometimes cystine-binding medications. Many people with cystinuria are misdiagnosed as having idiopathic kidney stones and receive wrong treatment for years.