Polygenic score

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A polygenic score is a single number that estimates how much a person’s genes, spread across thousands of places in the genome, contribute to a trait or the risk of a disease. It does not include environmental factors like diet or exercise, and it’s not a definitive diagnosis.

How it’s made
Scientists study large groups of people to find genetic variants, called SNPs, that are linked to a trait. Each variant has a small effect. A polygenic score adds up these effects across many SNPs, giving a total score that mirrors a person’s inherited tendency for that trait or condition.

What it’s used for
Polygenic scores can help predict the lifetime risk of complex diseases (such as heart disease, diabetes, and some mental illnesses) and other traits like height. They’re also used in animal and crop breeding to improve desirable features.

How strong the prediction is
Scores come from genome-wide association studies (GWAS). Bigger studies and better methods make them more accurate. However, the prediction is not perfect and often works better for people of the same ancestral background as the data used to build the score. Environmental factors still play a big role.

Limitations and cautions
- Most scores are less accurate for people of non-European ancestry because most data come from European populations.
- A high genetic risk does not guarantee disease; environment and lifestyle matter.
- A polygenic score is usually not a stand-alone test. It’s best used with age, weight, smoking, family history, and other risk factors.
- Results can be misinterpreted if not explained by a clinician or genetic counselor.

Clinical and ethical considerations
In medicine, polygenic scores may help tailor prevention and screening, and they can reduce some invasive tests in certain diseases. They’re not yet standard care for most conditions. In embryo screening, using polygenic scores raises ethical questions and safety concerns, and the practice is debated.

Real-world use
Today, many people can access polygenic scores through research studies or private genetic testing services that offer risk estimates for various diseases and traits. The scores are most informative when considered as part of a broader health picture.

Livestock and crops vs. humans
In animals and plants, a similar concept (genomic estimated breeding value) predicts the average performance of offspring. In humans, the goal is to estimate an individual’s disease risk or trait tendency rather than the average for offspring.

Looking ahead
The field is growing fast. Key goals include improving accuracy, making scores reliable across diverse populations, and combining genetic risk with other health information to better guide prevention and care.