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

Your kidneys filter phosphate continuously. But healthy kidneys also reclaim some of the phosphate they filter, returning it to your bloodstream in the right amount. That selective reabsorption happens through a protein called sodium-phosphate cotransporter, which is encoded by SLC34A1. It’s a precise valve, letting some phosphate back in and letting excess go to urine.

Variants in SLC34A1 can disrupt this balance. When this happens, your kidneys either reabsorb too much phosphate or lose too much. Roughly 5-10% of people carry variants that impair phosphate handling, and this directly affects the mineral composition of your urine. When phosphate is elevated in your urine, it creates the chemical environment where stones are more likely to form.

You might not feel this happening. There’s no obvious symptom of bad phosphate handling. But over time, your urine chemistry drifts into stone-forming territory. Combined with other factors, even a modest phosphate imbalance can tip the scales.

Deep inside your kidney tubules lives a protein called uromodulin. Its job is to coat the lining of your urinary tract, creating a protective mucus-like barrier. This barrier does two things: it prevents crystals from adhering to the tubule walls (the first step of stone formation), and it defends against UTI-causing bacteria. It’s like having a nonstick coating inside your pipes.

When you carry a UMOD variant that reduces uromodulin production, you lose that protection. Roughly 10-20% of people carry variants that lower uromodulin secretion, directly increasing both kidney stone risk and UTI susceptibility. With less protective coating, crystals are more likely to stick and grow. Your urinary tract also becomes more vulnerable to infection.

This explains why some people seem to get a double hit: recurrent kidney stones and recurrent UTIs. They’re not coincidences. They’re both consequences of the same genetic disadvantage. You might feel more prone to UTIs than your friends, and get kidney stones more easily. The common cause is sitting right in the UMOD gene.

Vitamin D doesn’t work until it’s activated. Your body converts it to a hormone-like form that circulates through your blood and enters cells through a receptor protein called the vitamin D receptor, or VDR. How well your cells respond to vitamin D depends partly on variations in the VDR gene. Some variants make cells respond more strongly to vitamin D; others make them less responsive.

This matters for kidney stones because vitamin D controls how much calcium your intestines absorb and how your kidneys handle calcium. People with certain VDR variants have altered calcium absorption and renal calcium handling, shifting their stone risk based on vitamin D status. If you have a variant that makes you hyper-responsive to vitamin D, even a modest amount of supplementation can push your urine calcium too high. If you’re hypo-responsive, you might need more vitamin D than standard recommendations suggest.

You might have gotten confusing advice about vitamin D: should you supplement, or is it unnecessary? The answer depends on your VDR variant and your current calcium metabolism. Guessing leads to either over-supplementation (raising stone risk) or under-supplementation (causing other problems).

Your body uses a molecular process called methylation to recycle amino acids and remove waste. A key step in this recycling involves MTHFR, an enzyme that converts a form of folate into its active form. This active form then helps your body process homocysteine, a compound that accumulates if your methylation cycle is slow. Elevated homocysteine isn’t just bad for your heart and brain; it affects your kidneys too.

Roughly 30-40% of people carry the MTHFR C677T variant, which reduces enzyme efficiency by 40-70%. When this happens, homocysteine builds up in your blood. Higher homocysteine is associated with impaired kidney function and increased stone risk. Additionally, slow methylation affects your ability to manage oxalate, another stone-forming compound.

You might feel the downstream effects: fatigue, brain fog, or a sense of sluggish metabolism. But the kidney impact is silent. Your homocysteine is rising, your kidney function is gradually declining, and your urine chemistry is shifting toward stone formation. None of this feels obvious until a stone actually forms.

Oxalate is a compound found in many foods: spinach, almonds, chocolate, tea. Your liver should break most of it down before it reaches your kidneys. The enzyme that does this breaking down is encoded by AGXT. It’s your primary defense against oxalate accumulation. When AGXT works well, even a high-oxalate diet isn’t a major problem for most people. When it doesn’t, even a low-oxalate diet may not be enough.

Loss-of-function variants in AGXT are rare, but when they occur, they cause a condition called primary hyperoxaluria. People with these variants have dramatically elevated oxalate, leading to severe calcium oxalate kidney stones and often early kidney disease. Your urine oxalate becomes so high that stones are almost inevitable, and they form repeatedly. Dietary oxalate restriction helps but often isn’t enough.

If you’ve been told you have primary hyperoxaluria, or if you have a family history of very early kidney stones (childhood or adolescence) and recurrent episodes, AGXT variants are a major concern. The stones form because your liver simply cannot process oxalate at the rate your body is generating it.

Cystine is an amino acid that your kidneys normally filter and reabsorb efficiently. A specific transporter protein, encoded by SLC7A9, is responsible for bringing cystine back into kidney cells so it doesn’t get wasted. When you carry loss-of-function variants in SLC7A9, your kidneys can’t reabsorb cystine properly. It accumulates in your urine instead.

When cystine builds up, it does something problematic: it has low solubility, meaning it readily crystallizes. Loss-of-function variants in SLC7A9 cause cystinuria, a rare but serious condition where cystine stones form repeatedly and are notoriously difficult to treat. These stones are not like calcium oxalate stones. They’re much harder, they recur more frequently, and standard stone-prevention strategies often fail against them.

If you have cystinuria, you’ve probably experienced this frustration: you follow dietary advice, drink water religiously, and stones still form. Your doctors might seem puzzled because standard interventions don’t work. That’s because cystine stones require specific, aggressive protocols. You’re not failing. The standard approach was never designed for cystinuria.