You've Passed Multiple Kidney Stones. Your Genes May Be Driving It.

Your kidneys filter phosphate constantly. In the nephron tubules, the SLC34A1 protein sits on the cell membrane and decides whether to reabsorb phosphate back into your bloodstream or let it spill into urine. This balance is critical: too little phosphate reabsorption and you lose what you need; too much and you accumulate excess that can crystallize into stones.

If you carry an SLC34A1 variant, your cells struggle to reabsorb phosphate efficiently. Approximately 5-10% of people carry a risk variant. This means phosphate accumulates in your urine, increasing the likelihood that it will combine with calcium to form stones. The more concentrated your urine, the faster crystals grow.

You might notice that despite managing your diet carefully, your stone risk remains high. You may also have other signs of phosphate handling issues: muscle weakness, bone pain, or a pattern of kidney stone recurrence every 1-3 years instead of being a one-time event.

Uromodulin is a protein secreted into the kidney tubules and urinary tract. It acts as a protective barrier, preventing mineral crystals from adhering to the tubule walls and growing into stones. It also helps defend against bacterial infection by coating the urinary epithelium. Think of it as a lubricant and antimicrobial shield for your urinary tract.

If you carry a UMOD variant, your kidneys secrete less protective uromodulin. Roughly 10-20% of the population carries a variant that reduces uromodulin secretion. Without enough uromodulin, mineral crystals stick to your tubule walls more easily, and your kidneys lose their first line of defense against both stone formation and infection. This makes you vulnerable to recurrent stones even if your diet is good and your electrolyte levels are normal.

You might experience not only recurrent kidney stones but also recurrent urinary tract infections. The two often come together in people with UMOD variants because the underlying problem is loss of the protective barrier that keeps both stones and bacteria at bay.

Your liver contains an enzyme called alanine-glyoxylate aminotransferase (AGXT). Its job is to metabolize glyoxylate, a compound produced during amino acid and vitamin C breakdown. If AGXT works normally, glyoxylate is converted into something your body can use or eliminate safely. If AGXT is defective, glyoxylate accumulates and gets converted into oxalate instead.

AGXT loss-of-function variants are rare but catastrophic for kidney stone risk. Fewer than 1% of people carry them, but those who do often have primary hyperoxaluria, a condition in which oxalate production is so high that your urine becomes saturated with calcium oxalate, and stones recur relentlessly, sometimes multiple times per year. Without treatment, this can progress to kidney failure.

If you have an AGXT variant, your stone history is likely severe: earliest onset often in childhood or young adulthood, stones composed primarily of calcium oxalate, rapid recurrence even with good dietary habits, and possibly a family history of kidney disease or early-onset stones.

The vitamin D receptor (VDR) is a protein in your cells that binds active vitamin D and turns on genes that regulate calcium absorption in the intestine and calcium reabsorption in the kidney. When VDR function is normal, your body carefully controls how much calcium enters your bloodstream and how much is excreted in urine.

If you carry a VDR variant, your cells may not respond as efficiently to vitamin D signaling. This can lead to two problems: either your intestines absorb too much calcium (which spills into urine and crystallizes), or your kidneys retain too much calcium. The result is hypercalciuria, or high urinary calcium, which is one of the strongest risk factors for calcium-based kidney stones. VDR variants are common, and the effect on stone risk is dose-dependent.

You might notice that your urine calcium stays elevated even when you limit dietary calcium. You may also have a personal or family history of osteoporosis or weak bones, because the same VDR dysfunction that raises urinary calcium can affect bone mineral density. Your stones are predominantly composed of calcium oxalate or calcium phosphate.

MTHFR is the enzyme that converts folate into its active methylated form, which your cells use to build DNA, regulate inflammation, and produce neurotransmitters. It’s also involved in regulating homocysteine, an amino acid that, when elevated, can damage kidney function and promote stone formation.

If you carry the MTHFR C677T variant, your enzyme efficiency is reduced by roughly 40-70%. Approximately 40% of the population carries this variant. Lower MTHFR activity means your cells cannot efficiently metabolize folate, and homocysteine can accumulate to levels that promote kidney damage and mineral dysregulation. Over time, elevated homocysteine is associated with endothelial dysfunction in the kidney and increased stone-forming risk.

You might have signs of impaired methylation: fatigue, brain fog, elevated homocysteine on bloodwork, or a history of cardiovascular issues. Your kidney stones may be accompanied by other signs of inflammatory kidney damage. The stone recurrence often worsens if you take synthetic folic acid supplements instead of methylated forms.

SLC7A9 encodes a transporter protein on kidney tubule cells that reabsorbs cystine, an amino acid, back into the bloodstream. When this transporter works normally, nearly all cystine is reclaimed and very little spills into urine. Cystine is unusual because it has very low solubility in urine; if too much accumulates, it crystallizes into notoriously difficult-to-treat stones.

If you carry an SLC7A9 loss-of-function variant, cystine cannot be reabsorbed efficiently and accumulates in your urine. This condition is called cystinuria and is rare, affecting roughly 1 in 7,000 people, but it is one of the most aggressive stone-forming conditions known. People with cystinuria recur almost inevitably and often form large stones that can obstruct the urinary tract and require surgical removal. Stones can form in childhood or recur throughout life.

If you have cystinuria, your stone composition is pathognomonic: pure cystine stones that appear radiolucent on imaging and often look like “stag horn” calculi. You likely have a lifelong history of stones, multiple surgical interventions, and a family history of early-onset stones because cystinuria is autosomal recessive.