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The muscle disease polymyositis is remarkably common in Kooikerhondjes. Kooikerhondjes with this disease have difficulty walking or swallowing (or both), which seriously threatens their well-being, and die prematurely. A DNA test, developed by veterinarians and researchers at the Expertise Centre of Veterinary Genetics at Utrecht ľ¹Ï¸£ÀûÓ°ÊÓ, makes it possible to detect carriers of the genetic defect that causes the disease, and eliminate it through selection in breeding.

Paul Mandigers, veterinary neurologist, Peter Leegwater, geneticist, and Yvet Opmeer, veterinarian and PhD student, found the responsible DNA defect after years of research. They compared the DNA of 106 healthy Kooikerhondjes with the DNA of 33 Kooikerhondjes with polymyositis, and found one striking difference. The sick animals were missing a large piece of DNA close to two important genes that play a role in immune system function.

Inflammation in the muscles

It was then investigated whether the absence of the piece of DNA affects the functioning of immune-related genes in white blood cells. For this purpose, blood was drawn from both sick and healthy Kooikerhondjes. The activity of the genes in the white blood cells was measured. It was found to be much higher in the Kooikerhondjes with the disease. This indicates that the immune system of the sick Kooikerhondjes overreacts to their own muscle cells, causing inflammation in the muscles.

DNA test

Based on these findings, the researchers developed a that determines whether a Kooikerhondje has the missing piece of DNA, and whether it carries one or two copies of the missing DNA. About 10% of dogs with two copies of the missing DNA and 1% of dogs with one copy will develop the disease. This suggests that there are probably other hereditary factors influencing the risk of the disease. Further research into these is currently underway.

Fit2Breed

Through collaboration with breeding guidance platform Fit2Breed, it is now possible to make a risk estimate for the likelihood of polymyositis in a litter of puppies after testing two potential parents. Thus, with good breeding policy, the disease can be banished from the breed.

Shohei Ohtani and his dog Decoy

The Dutch Kooikerhondje enjoys worldwide fame, partly due to the dog Decoy (short for Dutch Kooiker) of the very popular baseball player Shohei Ohtani of the Los Angeles Dodgers. Decoy was allowed to open a game in the autumn of 2023, and became world-famous doing so.

Plos Genetics

The came about thanks to the other authors: Frank van Steenbeek, Claudia Rozendom, Hille Fieten, Montse Diaz Espineira, Quirine Stassen, Peter van Kooten, Victor Rutten, Marjo Hytönen and Hannes Lohi. The support of The Society for the Dutch Kooikerhondje was also instrumental in this research.