SLC26A3 carrier status, and the Finnish condition that gets called something else
Untreated, this condition is dangerous in the first weeks of life. Treated, it is compatible with an ordinary one, and the treatment is salt. What stands between those two outcomes is usually the diagnosis, which is the part that keeps going wrong.
Also known as: SLC26A3 carrier, CCD carrier, congenital chloride diarrhoea, CLD, chloride-type congenital secretory diarrhea, Darrow-Gamble disease.
- Gene
- SLC26A3
- Inheritance
- Autosomal recessive
- Carrier frequency
- roughly 1 in 100 in eastern Finland, where it concentrates along a west-to-east gradient; rare in south-western Finland and very rare elsewhere in the world
What it is
Congenital chloride diarrhea is a recessive condition caused by changes in SLC26A3, the gene for an exchanger that sits in the lining of the ileum and colon and swaps chloride for bicarbonate. That exchange is how the gut reclaims chloride from intestinal contents. When it fails, chloride stays in the bowel, water follows it osmotically, and the result is watery diarrhea that is present from birth and does not stop. Because the loss begins before birth it also shows up in pregnancy, as dilated fetal bowel loops and excess amniotic fluid, which is sometimes read as intestinal obstruction.
The condition occurs worldwide but concentrates in a few populations, Finland among them, along with Poland, Kuwait and Saudi Arabia. Within Finland it follows a west to east gradient, so a family's origins inside the country change the picture considerably.
The reason to care about the name is that the condition is treatable and the treatment is unglamorous. Replacing what is being lost, as salt, keeps the chemistry in range. A 2025 Finnish study in PLOS ONE reports a median chloride dose of 3 mmol per kilogram per day among its patients, in line with clinical recommendations of 3 to 4. People on adequate substitution grow and develop normally. Without it, the losses of chloride, sodium and potassium in the newborn period are severe, which is why the interval before somebody works out what is happening is the part that carries the risk.
How it is inherited
The condition is autosomal recessive. A carrier has one changed copy of SLC26A3 and one working copy, the working copy exchanges enough chloride, and the carrier's bowel behaves normally. Carrier status is reproductive information: if a partner also carries an SLC26A3 change, each pregnancy has a one in four chance of an affected child.
In Finland the picture is dominated by one founder change. It is a deletion of three bases, which removes a single valine from the protein without disturbing the reading frame of everything after it, and Finnish patients characteristically carry it in both copies. The 2025 PLOS ONE study found all twenty-eight of its Finnish patients homozygous for it. One detail worth flagging for anyone who goes looking in the literature: the same change is written as V317del in some papers and as V318del in others. Current sources use the latter, including the 2025 study and the GeneReviews table of Finnish founder variants, which records it as c.951_953delGGT, p.Val318del. It is one variant described under two numbering conventions, not two variants.
Being a carrier does not cause bowel symptoms, and it is worth saying that clearly on a page about a condition whose defining feature is a common complaint. Chronic diarrhea is enormously more often something else. One changed copy of SLC26A3 is not a partial version of this condition.
What your raw DNA file can and cannot tell you
No consumer chip product reports this condition. 23andMe's published carrier status list, re-checked in August 2026, does not include congenital chloride diarrhea, so a 23andMe export says nothing about SLC26A3. Aimosti does not issue carrier status from a chip file either, for this gene or any other. The Finnish founder change is a three-base deletion, and a genotyping array asks which of two known letters sits at a fixed position, a question that is well posed for a substitution and badly posed for missing letters. A whole-genome VCF or gVCF is what our carrier module reads, and short-read sequencing calls small deletions of this size routinely.
There is a limit specific to this condition that deserves stating rather than burying. For most genes on the carrier panel, the person most interested in the answer is planning a pregnancy. Here there is a second reader: somebody, or somebody's child, with lifelong unexplained diarrhea who suspects the label they have been given is wrong. The literature contains case reports of exactly that, including congenital chloride diarrhea carried for years under a diagnosis of pseudo-Bartter syndrome, because the blood chemistry the losses produce can be read as a kidney problem rather than a gut one. If that describes you, be clear about what this page can offer. Carrier status is not a diagnosis, and a re-analysis of a consumer DNA file is not a substitute for a diagnostic work-up: the test that settles this is a stool chloride measurement alongside gene-targeted sequencing, ordered by a gastroenterologist. What a file can do is tell you the question is worth putting to one.
This product is not clinical carrier screening, and our panel deliberately omits conditions a short-variant file cannot call. For reproductive decisions the useful next steps are testing a partner and speaking with a genetic counsellor.
A genotyping chip reads only a few hundred thousand pre-selected positions, about 0.02% of your genome, chosen for common variation. It does not sequence the rest, so it cannot find the rare or novel pathogenic variants the clinical and carrier modules look for: a “no finding” from chip data means “this chip never looked”, far more so than with whole-genome sequencing. Chip data suits common-variant traits, pharmacogenomic tag SNPs, and haplogroup ancestry, not clinical or carrier screening.
Common questions
Does 23andMe test for congenital chloride diarrhea?
No. The published 23andMe carrier status list, re-checked in August 2026, does not include it, so its reports say nothing about SLC26A3. AncestryDNA does not report carrier status at all. That leaves a Finnish reader in the familiar position for this group of conditions: the file may contain the answer, but the product that generated it was never asked the question.
I have had unexplained diarrhea all my life. Could this be it?
It is possible and it is worth raising with a doctor, but the odds are against it and this page cannot narrow them. Congenital chloride diarrhea is rare, it is present from birth rather than starting later, and chronic diarrhea has many far commoner causes. What makes the question reasonable at all is that the condition has a documented history of being misdiagnosed, including as pseudo-Bartter syndrome, because the electrolyte disturbance it causes can look like a kidney problem. The way to settle it is a stool chloride measurement and gene-targeted sequencing arranged by a gastroenterologist, not a carrier result.
Is congenital chloride diarrhea treatable?
Yes, and that sets it apart from most conditions on a carrier panel. Treatment is salt substitution, replacing the chloride and other electrolytes being lost, taken lifelong. A 2025 Finnish study reports a median dose of 3 mmol of chloride per kilogram per day, consistent with published recommendations of 3 to 4. Adequately treated people grow and develop normally. The danger sits in the newborn period before anyone has identified what is happening.
A study linked this condition to the cystic fibrosis gene. What does that mean for me?
It means less about you than the headline suggests. The 2025 PLOS ONE study found that certain rare variants near and within CFTR, the cystic fibrosis gene, are enriched on the Finnish chromosomes that carry the congenital chloride diarrhea founder change. The variants it identified sit in introns and in neighbouring sequence rather than in the protein-coding parts of CFTR. It is an observation about which stretches of DNA travelled together through Finnish population history, and possibly about factors that modify how the bowel condition presents. It is not a finding that carriers of one condition are carriers of the other, and it does not change what an SLC26A3 carrier result means.
Why is the founder variant written two different ways?
Because sources number the affected residue differently. The three-base deletion that accounts for Finnish cases appears in the literature as V317del in some papers and as V318del in others. Current references use V318del, including the 2025 Finnish study and the GeneReviews table of Finnish founder variants, which writes it as c.951_953delGGT, p.Val318del. Both names refer to the same deletion of a single valine from the same protein. If you are comparing sources and see both, you are looking at one variant under two conventions rather than at two separate findings.