Kooikerhondje
The tested variant with the highest allele frequency is Chondrodystrophy and Intervertebral Disc Disease Risk, at 56% among the 197 Kooikerhondjes tested (Donner 2023; gene copies, not dogs), then Cystinuria Type I-A (17%).
Which disease variants turn up in Kooikerhondjes?
From a panel of 250 Mendelian-disease variants screened in 1,054,293 dogs (Donner et al. 2023), 4 turn up in Kooikerhondjes at observable frequency. The figure beside each is its allele frequency. Of the gene copies tested in this breed, the share that carry the variant. Every dog carries two copies, so this is not the share of dogs. It is not clinical risk. Most recessive variants require two copies for disease expression; many dominant variants show incomplete penetrance. Read this as a population fingerprint of what's in the gene pool, not a per-dog prediction.
FGF4what this gene does
FGF4 influences leg length by affecting bone growth, leading to shorter legs in certain breeds.
For your dog: If your dog is from a breed known to carry this gene, it's worth discussing spinal health with your vet, but being a carrier doesn’t guarantee problems.
SLC3A1what this gene does
SLC3A1 is a gene that helps transport certain amino acids in the kidneys. It plays a key role in preventing the buildup of cystine, which can form stones.
For your dog: If your dog is from a breed known to carry SLC3A1 variants, it’s worth discussing cystinuria risks with your vet, especially if urinary issues arise.
SOD1what this gene does
SOD1 is a gene that helps protect cells from damage caused by harmful molecules called free radicals.
For your dog: If your dog is a carrier of SOD1 variants, it's worth discussing with your vet, but remember carrier status doesn't mean your dog will get the disease.
PDE6Bwhat this gene does
PDE6B is a gene that helps control how the eye processes light signals, crucial for normal vision.
For your dog: If your dog is from a breed known to carry PDE6B mutations, it's worth discussing vision health with your vet, especially if you notice any changes in sight.
What these results mean for a Kooikerhondje
56.1% of Kooikerhondjes in the Donner 2023 cohort carried it (n=197).
- Two extra copies of a growth gene, FGF4, shape dog legs and spines. The one on chromosome 12 is the one tied to disc disease; the one on chromosome 18 shortens legs.
OMIA 000157-9615
“Two FGF4 retrogenes (FGF4L1 on chromosome 18 and FGF4L2 on chromosome 12) have been identified to cause dwarfism across many dog breeds.” OMIA 000157-9615
“Brown et al. (2017) reported that an FGF4 retrogene insertion in chromosome CFA12” OMIA 000157-9615
- Carrying it raises risk. It does not say which dog will have a disc problem. In Dachshunds researchers found the test is not a valid risk indicator on its own.
OMIA 000157-9615
“the FGF4 retrogene insertion on CFA12 is not a valid risk indicator on its own” OMIA 000157-9615
What to do
Ask your veterinarian what a carrier result changes for your dog. What lowers risk in a carrier is not established in the sources this page draws on.
No test, or a mix
Without a test nobody can say whether a dog carries it. Leg length alone does not tell you: the disc-disease copy and the short-leg copy are different insertions.
16.5% of Kooikerhondjes in the Donner 2023 cohort carried it (n=200).
- The kidneys fail to reclaim an amino acid called cystine, which can form crystals and stones in the urine and block the urinary tract.
OMIA 000256-9615
“Cystinuria, type 1 - A is an inherited defect that causes failure of reabsorption of cystine in the proximal renal tubule, leading to cystine precipitation in the urine. Formation of crystals and calculi lead to urolithiasis and urinary tract obstruction.” OMIA 000256-9615
What to do
Straining to urinate, or passing little or no urine, needs a veterinarian the same day.
No test, or a mix
Without a test nobody can say how many copies a dog has.
For researchers Population genetics, disease models and every recorded condition Open the research detail for the Kooikerhondje
Where every number on this page came from.
This page draws on one primary data source. Allele frequencies and sample sizes come from Donner et al. 2023 (CC-BY-4.0), a direct-to-consumer screening cohort, graded Limited as a study design because the dogs were tested at their owners' choice. No genotyped research dogs of this breed are in the three open releases the atlas reads, so the population-genetic sections other breed pages carry are absent here for that reason, not hidden. Conditions recorded for the breed come from OMIA.
What this page does not yet have. Inheritance modes and per-disease penetrance evidence from Donner 2023 are in the structured data for every variant the panel covers. Mondo, OMIM, Ensembl, and HGNC cross-references live on the gene and disease pages this page links to, rather than being repeated here. What is still absent from this breed page is anything not in the cited panel, and each such gap carries its cause where it appears.
How to cite this page. Cite Donner et al. 2023 (doi:10.1371/journal.pgen.1010651) for every frequency on this page, and OMIA for each condition, with the sample size shown beside the figure.
Some things about living with a kooikerhondje never make it into a database. Add what you know as a Keeper, in your words →
Lived experience, kept beside the science.No kooikerhondjes are in the atlas yet. Yours would be the first star for the breed.
Every kooikerhondje added sharpens the breed's genetic neighborhood. Enrollment is free. The data stays open. The star is permanent.
- Donner J, Freyer J, Davison S, Anderson H, Blades M, Honkanen L, et al. (2023). Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLOS Genetics 19(2):e1010651. doi:10.1371/journal.pgen.1010651
- Brundage DM (2026). CanVAS: A Harmonized and Imputed Canine Variant Atlas. bioRxiv. doi:10.64898/2026.04.13.718238
- Nicholas, F.W., Tammen, I., & Sydney Informatics Hub. (2026). Online Mendelian Inheritance in Animals (OMIA) [dataset]. The University of Sydney. https://omia.org. doi:10.25910/2AMR-PV70 (retrieved April 2026).