SLC34A3

If you have had recurrent kidney stones, unexplained low phosphate on a blood test, or a family member with bone disease that nobody could explain, this gene is one of the first places a specialist would look. SLC34A3 (solute carrier family 34 member A3) carries the instructions for a kidney protein that decides how much phosphate your body holds onto versus loses in your urine.

When this gene does not work properly, phosphate leaks into the urine, vitamin D activity climbs, and calcium spills into the urine too. The downstream consequences can show up as kidney stones, calcium deposits in the kidney, soft or brittle bones, or short stature in childhood. Testing the gene can give you a clear cause for symptoms that often get labeled idiopathic for years.

What the Gene Actually Does

SLC34A3 codes for a transporter called NaPi-IIc (sodium-dependent phosphate cotransporter type 2c), which sits on the surface of cells in the proximal tubule, the part of the kidney that decides what to keep and what to send out as urine. Its job is to pull phosphate back into the body alongside sodium. Phosphate is the mineral that, with calcium, gives bones their strength and powers nearly every reaction inside your cells.

When both copies of the gene carry damaging changes, the transporter cannot do its job. Phosphate slips into the urine, blood phosphate drops, and the body responds by making more active vitamin D (called 1,25-dihydroxyvitamin D). That extra vitamin D pulls more calcium out of your gut, which then floods the urine. Over time, those extra calcium-laden filtrates can crystallize into stones or deposit inside the kidney tissue itself.

Hereditary Hypophosphatemic Rickets with Hypercalciuria

The classic disease caused by two damaging SLC34A3 variants is hereditary hypophosphatemic rickets with hypercalciuria, or HHRH. The biochemical fingerprint is consistent and recognizable: low phosphate in the blood, low tubular reabsorption of phosphate, elevated active vitamin D, low or normal parathyroid hormone, low or normal FGF23, and too much calcium in the urine.

In a study of 304 people with HHRH and related variants, biallelic carriers showed high rates of rickets or bone deformity, fractures, short stature, kidney stones, and kidney calcium deposits. Heterozygous carriers, who have just one damaged copy, often had milder versions of the same picture: hypercalciuria, sometimes low phosphate, often kidney stones, and occasionally reduced bone density.

Kidney Stone Risk in Carriers

Even people with only one damaged SLC34A3 copy can have meaningful kidney problems. In a large analysis of UK Biobank participants, rare damaging variants in SLC34A3 were enriched in adults with urinary stone disease and helped explain part of the heritability that earlier genetic studies could not account for.

Among children with kidney stones or kidney calcium deposits sent for broad genetic testing, SLC34A3 emerged as one of the most common culprits, and genetic testing gave a diagnosis in roughly a third of cases overall. If you have had repeated stones starting in childhood or early adulthood, especially with elevated urinary calcium, an inherited problem in this transporter belongs on the differential.

Chronic Kidney Disease Risk

The damage does not stop at stones. In a multicenter study of 113 carriers of pathogenic SLC34A1 and SLC34A3 variants, adult biallelic SLC34A3 carriers had about six times the prevalence of chronic kidney disease compared with the general population. Long-standing high urinary calcium, calcium deposits in the kidney tissue, and repeated stone events appear to slowly erode kidney function over the years.

What this means for you: a genetic answer is not just academic. People who learn early that their kidney stones or low phosphate trace back to SLC34A3 can start hydration, dietary, and medical strategies designed to protect long-term kidney function, not just treat the next stone.

Bone Disease and Fractures

Because phosphate is structural to bone, chronic phosphate wasting can produce rickets in children and osteomalacia, or soft bone, in adults. People with HHRH commonly present with bone pain, fractures, bowed legs, short stature, or in adults, fragility fractures that get misread as early osteoporosis.

Late presentations exist too. A case report described an adult with severe stones, multiple fractures, and low bone density whose true diagnosis was late-onset HHRH from an SLC34A3 mutation. The pattern matters: if your bone density is low and your blood phosphate is also low, generic osteoporosis treatment is the wrong tool.

The Phenotype Can Be Variable

One quirk of SLC34A3 is that even people in the same family with the same variants can present very differently. Some have severe bone disease as toddlers. Others have nothing more than mildly elevated urinary calcium and a single stone in their forties. The reasons include the type of variant, whether it is on one or both copies, and modifier genes elsewhere in the genome.

Digenic combinations also exist. In a series of six people, heterozygous variants in both SLC34A3 and the related gene SLC34A1 produced more severe disease than a single hit in either gene alone. If your family history shows mixed presentations of stones, low phosphate, or fractures across generations, the inheritance pattern is rarely as simple as a single mutation.

Reconciling the Variable Picture

This is not a yes-or-no biomarker. SLC34A3 is a phenotype-modifying gene, where the same DNA letter change can mean different things in different bodies. A normal urine calcium today does not rule out future stones, and a single damaged copy does not guarantee disease. The result is most useful when read alongside your serum phosphate, urinary calcium, 1,25-dihydroxyvitamin D, parathyroid hormone, and a careful look at your bone and kidney imaging.

Tracking Your Trend

Your SLC34A3 genotype does not change, but its biochemical consequences do. The biomarkers that matter, including serum phosphate, urinary calcium, active vitamin D, and kidney function, drift over time based on diet, hydration, treatment, and the quiet progression of any kidney damage. A single normal blood phosphate level after a phosphate-rich meal can lull you into thinking nothing is wrong.

If you carry a damaging SLC34A3 variant, plan on getting a baseline serum phosphate, 24-hour urinary calcium, active vitamin D, and a kidney imaging study, then repeating the biochemical labs every 6 to 12 months. Trends matter more than any single number. A urinary calcium that has climbed steadily over three years is a warning even if today's value is within range, and a kidney imaging study every few years catches calcium deposits before they cause symptoms.

What to Do With an Out-of-Pattern Result

If your SLC34A3 result shows a pathogenic or likely pathogenic variant, the next step is biochemical confirmation: serum phosphate with tubular reabsorption calculation, 24-hour urinary calcium and phosphate, 1,25-dihydroxyvitamin D, parathyroid hormone, FGF23, and bone density imaging. Pair the genetic result with these labs to understand what your body is actually doing.

From there, the right specialist depends on what you find. A nephrologist takes the lead if stones or kidney calcium deposits dominate, an endocrinologist if low phosphate and bone disease dominate, and a geneticist if your family wants cascade testing to identify silent carriers. Cascade testing matters because relatives often carry the variant without knowing it, and they can adopt protective strategies before stones or kidney damage develop.

Why a Single Lab Panel Can Miss It

A standard chemistry panel will not flag this gene. Phosphate is not always part of routine bloodwork, and 1,25-dihydroxyvitamin D is rarely measured outside of specialty workups. Kidney function tests like creatinine can look completely normal for years before any decline shows up. If you or a family member have a story of unexplained stones, low phosphate, or fractures, ordinary labs are not enough to rule out a genetic phosphate-wasting disorder.