NPHS1 carrier status, and the founder variant that is the wrong shape for a chip

This is the condition with Finland in its name. It is also the one where the reason a consumer chip cannot help is not the usual reason, and the difference is worth understanding before you decide what your file is capable of answering.

Also known as: NPHS1 carrier, CNF carrier, Finnish type congenital nephrosis, nephrin deficiency.

Gene

NPHS1

Inheritance

Autosomal recessive

Carrier frequency

roughly 1 in 50 in Finland, one of the more common Finnish founder conditions; rare elsewhere in the world

What it is

Congenital nephrotic syndrome of the Finnish type is a recessive kidney condition caused by changes in NPHS1, the gene for nephrin. Nephrin is a structural protein of the podocyte, the cell that forms the kidney's filtration barrier, and it sits at the slit diaphragm, the narrow gap through which filtrate has to pass. Without working nephrin the barrier leaks, and it leaks protein on a scale that begins before birth. MedlinePlus records that symptoms appear between birth and three months of age.

The Finnish part of the name is earned by the numbers rather than by sentiment. MedlinePlus puts the condition at roughly 1 in 10,000 children in Finland against 1 to 3 per 100,000 children worldwide, which is a difference of one to two orders of magnitude depending on which end of the global range you take. It also states that NPHS1 changes cause all cases of the Finnish type specifically, while congenital nephrotic syndrome as a whole has several genetic causes. The GeneReviews overview of genetic steroid-resistant nephrotic syndrome puts NPHS1 alongside LAMB2, NPHS2 and WT1 as the four genes accounting for more than 80% of all congenital nephrotic syndrome.

One feature of this condition matters for anybody reading a carrier page about it. Nephrin's job is confined to the kidney, and NPHS1 disease is correspondingly non-syndromic: it does not come with findings in other organ systems. Combined with an onset measured in weeks rather than decades, that means an adult reading this page is a carrier or is unaffected. There is no version of this condition that has been quietly present all along and is about to declare itself.

How it is inherited

The condition is autosomal recessive. A carrier has one changed copy of NPHS1 and one working copy, the working copy makes nephrin, and the filtration barrier is built normally. Carrier status is information about reproduction: if a partner also carries an NPHS1 change, each pregnancy has a one in four chance of an affected child.

The Finnish frequency comes from founder history, and two founder changes account for most of it. The larger is catalogued in ClinVar as NPHS1 c.121_122del and has been known in the literature for decades as Fin-major. GeneReviews, in its table of founder variants common in the Finnish population, puts it at 78% of disease-causing alleles here, with a second change, Fin-minor, at a further 16%. ClinVar classifies Fin-major as pathogenic and records an allele frequency of about 0.011 among Finnish Europeans, which is why a carrier rate that would be startling elsewhere is unremarkable in Finland.

What that variant is, at the level of DNA, is the thing this page turns on. It is a deletion of two bases. Removing two bases from a coding sequence shifts the reading frame for everything downstream, so the protein is truncated early and there is no functional nephrin at the end of it. ClinVar records the consequence as p.Leu41fs, a frameshift beginning at codon 41 of a protein that is over twelve hundred amino acids long.

What your raw DNA file can and cannot tell you

Here is why that detail earns a section. A genotyping chip works by asking, at each of a few hundred thousand fixed positions, which of two known bases is present. That question is well posed for a substitution, where one letter has been swapped for another. It is poorly posed for a deletion, where the letters are not there to be read, and arrays are correspondingly unreliable at calling small insertions and deletions even when a probe has been designed for one. So the commonest founder variant behind Finland's signature inherited kidney condition is not merely absent from consumer arrays, which it is. It is the wrong shape of variant for the method. This is a genuinely different failure from the one on our aspartylglucosaminuria page, where the founder variant is an ordinary substitution that an array could type perfectly well and simply was never asked to. Two Finnish founder conditions, two unrelated reasons a chip export answers neither.

23andMe's published carrier status list, re-checked in August 2026, does not include congenital nephrotic syndrome of the Finnish type, so the question does not arise for that product in practice. Aimosti does not issue carrier status from a chip file for this gene or any other. A whole-genome VCF or gVCF is what our carrier module reads, and short-read sequencing calls small deletions of this kind routinely, so a file of that sort can carry a real answer about NPHS1 where a chip export cannot carry one at all. That is the honest boundary between the two file types on this particular gene, and it is sharper here than almost anywhere else on the panel.

This is not clinical carrier screening and it is not a substitute for a validated, gene-targeted carrier test arranged through a clinic. A re-analysis of a file you already have can tell you whether the question deserves a proper test. If a result points at NPHS1 and you are planning a pregnancy, the next steps are testing the partner and speaking with a genetic counsellor. If a child is already unwell, that is a paediatric nephrology question and nothing on this page belongs in it.

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.

Check what your file covers

Common questions

Sources

• MedlinePlus Genetics: Congenital nephrotic syndrome
• Finnish Disease Database (findis.org)
• ClinVar: NPHS1 c.121_122del (Fin-major), Finnish congenital nephrotic syndrome
• GeneReviews: Genetic Steroid-Resistant Nephrotic Syndrome Overview
• GeneReviews: Genetic Disorders Associated with Founder Variants Common in the Finnish Population