Most people globally face 'high genetic risk' for three common diseases: Study

Most people worldwide could be categorised as having a high genetic risk for three of 28 common conditions, including diabetes, cardiovascular disease and schizophrenia, even if they might not develop them, a new study has found.

Researchers, led by the UK's University of Exeter, described the 'average' human genome, finding that everyone, regardless of their current health status, could be considered at risk for numerous conditions based on their genetics alone.

Every person's genome, or the average human genome, contains around five million variants, or DNA locations that differ between individuals, the findings published in the journal Genome Medicine reveal.

The locations include around 10,000 variants that alter gene sequences, which can have positive or negative effect, ranging from lactose intolerance to drug response, though are often biologically neutral, they show.

Each person also carries between one and three rare variants previously shown to cause serious genetic diseases, and another 50 rare variants that are currently of uncertain clinical relevance, the researchers found.

The team analysed data from two major population biobanks -- the UK Biobank and the US' All of Us -- that include whole genome sequencing, covering nearly one million individuals.

Senior author Caroline Wright, from the University of Exeter, said, "Whole genome sequencing has become such an important tool in diagnosing genetic disease, and we're increasingly moving towards genetic screening for predicting disease."

"Yet most people are unaware of just how much genetic variation is present in every genome. Actually, variation is the norm. For the first time, our study outlines what to expect in the average human genome, which can benefit clinicians and patients across the word in understanding, interpreting and contextualising genomics," Wright said.

The researchers also analysed numerous polygenic risk scores, which consider all known genetic factors to calculate a person's future risk of developing a disease.

"... applying polygenic scores (PGS) for 28 common diseases within UKB (UK Biobank), we estimate that the average person is in the top 10 per cent for (nearly) three conditions, and around one in five people are in the top one per cent for at least one PGS," the authors wrote.

"Importantly, we found that everyone carries a small number of genetic variants linked to disease, although many of these will not actually cause disease in that individual," Wright said.

The senior author added, "It is therefore crucial to consider context when interpreting findings from genetic testing, including symptoms or family history of disease as well as other clinical and environmental risk factors. Our findings also provide important context for professionals who are interpreting genetic testing results or commissioning genetic screening programmes."

Although the studies are large, participation is skewed towards people of Western European origin, and the researchers acknowledged the need for data from more diverse populations to further improve understanding and impact.