- DNA
- Diagnostics
18. 8. 2026
Polygenic Score in Horses: When a Single Mutation is not Enough
Many people associate the term genetics with a simple and direct cause-and-effect relationship: one gene, one mutation, one trait. However, the genetic outcomes for many traits, such as performance, behavior, athleticism, disease susceptibility, and temperament, cannot be simplified in this way, as these traits are not defined by a single mutation but by hundreds to thousands of minor factors, each with its own tiny effect on the outcome. Individually, many of these variants have only a small effect, but when we look at them as a whole, they become more meaningful.
What we just described is the basis of a polygenic score (PS), a term researchers use to refer to the sum of these combined signals. While studying these traits, researchers do not look for a single responsible gene but rather scan the genome as a whole, looking for small, individual signals that they sum up to obtain a number – a polygenic score for a specific individual.
What does such a number say? It’s an estimate of an individual’s genetic predisposition to a trait or disease. It certainly does not predict the future of a particular horse – a horse with a high score may not express the trait, and one with a low score may not necessarily avoid it. We are only talking about probability here - at most.
The process of obtaining the score starts with a genome-wide association study (GWAS). In the study, researchers compare genomes of two groups of horses. They can, for example, compare sick horses to healthy ones, top-performing sport horses to their peers, or horses exhibiting certain behaviors to those exhibiting different behaviors. This comparison is used to identify variants whose prevalence differs between the two groups. Alternatively, for quantitative traits like height or speed, researchers analyze a continuous population scale rather than comparing two distinct groups.
The catch is that the individual mutations typically have only a small effect on their own, which means that a large number of horses is usually needed for a study like this before clear trends emerge. Polygenic research is therefore necessarily a long-term process. For comparison, human genetic research has a significant advantage, as there are already many databases containing hundreds of thousands, even millions, of human genetic records that can be used for such studies. However, the clinical relevance of the polygenic scores remains a subject of discussion.
Another catch with horses and some other animal species is the wide variety of breeds, which can be genetically very different, making research more complicated.
So far, we don’t have sufficient data to clearly link individuals' genetic information to accurate and up-to-date health status and performance records. This remains the greatest bottleneck in solving the issue.
