polygenic score
A polygenic score is a single number that adds up the small genetic nudges a person carries for some trait. Each variant linked to the trait by large studies is given a weight reflecting its estimated effect, and the score tallies how many trait-raising versions an individual has across all of them — a genetic running total rather than a verdict on any one gene.
The weights come from genome-wide association studies, where the effect of each common variant on a trait is estimated across huge samples. Summed over hundreds of thousands of positions, the score arranges a population along a continuum: people at the high end carry, on average, a heavier genetic loading for the trait than those at the low end. For complex traits, this is the closest thing to reading genetic predisposition off the genome.
The honest caveats are central, not footnotes. A polygenic score is a probabilistic, population-level summary: it shifts average risk between groups but predicts poorly for any single person, captures only part of the heritability, and ignores environment entirely. Crucially, scores built mainly in one ancestral population transfer poorly to others, because the patterns of correlation between variants differ — a limitation that demands caution before any individual or clinical use.
A coronary-disease polygenic risk score can flag the small fraction of people whose inherited loading rivals that of carriers of rare high-risk mutations, helping prioritise earlier lifestyle attention — without ever predicting any one person's fate with certainty.
A relative ranking, not an individual prophecy.
When the trait is a disease, the same idea is called a polygenic risk score. It estimates relative genetic predisposition, not a diagnosis, and is best read alongside family history and environment rather than alone.