SLC39A8 Genotype

If you have ever wondered why two people eating the same diet, exercising the same way, and showing identical cholesterol numbers can still end up with very different health trajectories, genes like SLC39A8 (Solute Carrier Family 39 Member 8) are part of the answer. This gene builds a tiny channel on your cells called ZIP8 that pulls zinc, manganese, and iron from your blood into your tissues. A common spelling change in this gene quietly shifts how well that channel works, and that shift has been linked to a surprisingly wide set of conditions, from Crohn's disease to schizophrenia to liver inflammation.

This is a once-in-a-lifetime test that reads a fixed part of your DNA. Your result will not move with diet, exercise, age, or supplements. What it can give you is a stable piece of inherited context, a baseline understanding of whether you carry a variant that has been tied in human studies to higher risk for certain inflammatory, neurologic, and metabolic conditions, so you can monitor accordingly.

What This Gene Actually Does

SLC39A8 codes for a protein called ZIP8, which sits on the surface of your cells and acts like a doorway for essential trace minerals, primarily manganese, zinc, and iron. Manganese in particular is required for enzymes that build complex sugar coatings on proteins (a process called glycosylation) and for enzymes that protect your cells from damage. The gene is active in the liver, gut, brain, lungs, placenta, and many other tissues.

The most studied variant in this gene is a single-letter change called rs13107325, which swaps one amino acid for another at position 391 of the protein (Ala391Thr, often written as A391T). In laboratory studies, this change appears to modestly reduce how efficiently ZIP8 imports manganese into cells, a much milder effect than the severe rare variants that nearly abolish transport. Even so, people who carry this common variant tend to have lower manganese levels in their blood and brain, and altered sugar-coating patterns on the proteins circulating in their blood.

Crohn's Disease and Gut Inflammation

One of the most consistent findings about the A391T variant is its connection to Crohn's disease, an inflammatory bowel condition. In a large genetic study of more than 16,000 people, the variant was significantly more common in those with Crohn's disease, and it was also tied to changes in the gut microbiome composition. A follow-up study including both Crohn's patients and healthy controls again linked the variant to Crohn's risk, but found that in healthy carriers it did not noticeably reshape gut bacteria.

What this means for you: if you carry this variant and have a family history of Crohn's disease or other inflammatory bowel conditions, this is one inherited factor pulling your risk upward. It does not guarantee you will develop the disease. Many carriers never do. But it is a reason to take new digestive symptoms seriously rather than waiting them out.

Brain, Behavior, and Schizophrenia Risk

The same A391T variant has been repeatedly tied to schizophrenia risk in large genome-wide studies. Research on patients carrying the variant shows reduced manganese levels in the brain and changes in how proteins are built. A separate analysis combining about 1,700 adolescents in the discovery sample with replication in nearly 8,700 adults found that carriers had larger gray matter volume in a brain region called the putamen, which sits in the deep part of the brain involved in movement and learning, though this difference was weaker in people already diagnosed with schizophrenia.

Beyond schizophrenia, a wide-ranging analysis of the variant's downstream effects also tied it to higher risk of cerebrovascular disease, meaning conditions affecting blood vessels in the brain. A systematic review of tinnitus also identified SLC39A8 among the genes potentially contributing to shared neural functions in people experiencing ringing in the ears.

Heart and Cardiovascular Risk

In a study drawn from a trial of more than 18,000 patients with acute coronary syndrome, with genetic analysis performed on a subset of about 9,200, the SLC39A8 A391T variant was associated with higher levels of NT-proBNP (N-Terminal Pro-B-Type Natriuretic Peptide), a blood marker of heart strain, and with a higher risk of cardiovascular death over follow-up. The original authors cautioned that, given the variant's many downstream effects, NT-proBNP itself may not be the direct driver of that mortality signal. A separate large genetic study identified the SLC39A8 region as one of four new locations in the genome influencing blood lipid levels and coronary artery disease risk.

A 2025 analysis of more than 276,000 people in the UK Biobank found that higher dietary manganese intake was associated with measures of better cardiovascular health, and may help offset some of the risks linked to the A391T variant. If you carry this variant, the cardiovascular signal is one more reason to keep ApoB, blood pressure, and inflammation markers tracked closely.

Liver Inflammation

In a Danish study of roughly 1.2 million people, the A391T variant was associated with slightly higher plasma alanine transaminase (ALT, a blood enzyme that rises when liver cells are stressed) and with imaging markers suggesting liver inflammation. The same study did not find an increased risk of cirrhosis or liver cancer in carriers. Translation for the reader: this variant may push the dial a little on liver stress markers, but the most severe liver outcomes do not appear to follow.

Skeletal and Musculoskeletal Findings

A genetic analysis of more than 3,000 people identified the A391T variant as a risk factor for severe adolescent idiopathic scoliosis, a sideways curvature of the spine that develops during adolescence. A follow-up study in a Chinese Han population of nearly 2,000 people did not detect the A391T variant itself in that group, but instead linked a different coding variant in the same SLC39A8 gene to scoliosis risk, supporting the broader role of this gene across populations even when the specific variant differs. Carriers of A391T also showed up at younger ages of diagnosis for atraumatic rotator cuff tears in a study of 336 shoulder patients, suggesting the variant may also affect connective tissue resilience.

Severe Variants: SLC39A8-CDG

Beyond the common A391T variant, rare and more severe spelling changes in both copies of SLC39A8 cause a serious inherited condition called SLC39A8-CDG (Congenital Disorder of Glycosylation). Children with this condition can develop severe developmental delay, dystonia, seizures, hearing loss, and brain imaging that resembles Leigh syndrome. The good news is that oral galactose with manganese supplementation has been shown to improve both biochemical markers and some clinical features in affected children, making genetic diagnosis directly actionable. This is rare, but it is one reason why this gene matters in pediatric clinical genetics.

Reconciling the Wide Range of Effects

It might seem strange that one gene variant could connect to conditions as different as Crohn's disease, schizophrenia, heart strain, and scoliosis. The unifying thread is manganese. Manganese is required by enzymes that build the sugar coatings on many of your body's proteins, including proteins on the surface of immune cells, in cartilage, and in the brain. When the ZIP8 doorway works less efficiently, those sugar coatings get built less completely, which appears to affect tissues across the body in different ways. This is not a single disease marker. It is an inherited setting that nudges several different systems at once.

One-Time Test, Lifetime Result

Because this is a genetic test, your result does not change. You inherited your SLC39A8 genotype from your parents and you will pass it on to any biological children. There is no point in retesting the gene itself unless your initial result was uncertain or used a less reliable method. What does need ongoing tracking are the downstream markers this variant influences: high-sensitivity CRP (hs-CRP, a marker of inflammation), ALT and other liver enzymes, ApoB and standard lipid markers, and NT-proBNP if you have cardiovascular concerns. If you carry the A391T variant, treat those tests as the moving picture and your SLC39A8 result as the fixed context behind it.

What to Do If You Carry the Variant

Carrying the A391T variant does not mean any of the linked diseases will develop. Most carriers live without ever experiencing Crohn's disease, schizophrenia, or a cardiac event. But it does shift your prior probability, and that shift is worth knowing. If you carry one or two copies, the practical next steps are to set a baseline on the downstream markers above, pay closer attention to gut symptoms or family patterns of inflammatory bowel disease, keep cardiovascular risk factors tightly managed, and discuss with a genetic counselor whether biological relatives might also benefit from learning their genotype.

When Results Can Be Misleading

Genetic tests have their own set of confounders that differ from blood-chemistry tests.

• Variant panel coverage: the test only detects the specific variants the assay is designed to detect. A negative result for the common A391T variant does not rule out rarer, potentially more impactful variants elsewhere in the SLC39A8 gene.
• Ancestry differences: allele frequencies for SLC39A8 variants differ across populations. The A391T variant, for example, is rare or absent in some East Asian groups, so the clinical meaning of a result depends on your background.
• Variants of uncertain meaning: the assay may report a rare spelling change with no clear clinical interpretation. This is not the same as carrying a known disease variant.
• Direct-to-consumer versus clinical-grade results: a 23andMe-style report may reference rs13107325 but uses chip-based methods that can occasionally misread variants. Clinical-grade confirmation is appropriate before making major health decisions.