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Genes play a larger overall role than environment or socioeconomic factors in causing human diseases, according to a comprehensive analysis of health insurance data, including a large cohort of twins, according to a Nature Genetics study published Monday.

What's new: Nearly 40% of human diseases can be linked to genetic factors, while 25% are at least partly driven from the environment. However, socioeconomic factors only play a modest role, the scientists find.

Why it matters: Information on what causes diseases — or even what doesn't cause diseases — can inform future research, study author Chirag Lakhani tells Axios.

"We want to know: Would genetics be a more helpful line of research or not," Lakhani says. "If not, what are the environmental things we should be trying to measure."

What they did: Using de-identified data from Aetna insurance (which didn't fund the study), the team from Harvard Medical School and Australia's University of Queensland examined records from nearly 45 million Americans, including more than 56,000 twin pairs and 724,000 sibling pairs.

  • They analyzed heritable and environmental factors across 560 common conditions and diseases spanning 23 categories, ranging from cardiovascular illness and neuromuscular diseases to skeletal conditions.
  • They extrapolated environmental factors such as air pollution levels, climate conditions and socioeconomic status from the patients’ zip codes.
  • They also looked at diseases by monthly health care spending.
  • They compared their heritability findings (called CaTCH) with that of another large data dive into twin sets from 2015 (called MaTCH), although the ages of twins and the specific conditions differed somewhat.

What they found: Nearly 40% of the diseases in the study (225 of 560) had a genetic component, while 25% (138 of 560) partly stemmed from a shared living environment (conditions from sharing the same household, social influences, etc.)

  • Heritability shows the greatest influence on cognitive disorders (4 out of 5 diseases). It has the least amount of influence on connective tissue diseases (2 out of 11).
  • Shared environmental influence has the highest impact on eye disorders (27 out of 42), followed by respiratory diseases (34 out of 48 conditions). It has the least effect on reproductive illnesses (3 out of 18) and cognitive conditions (2 out of 5).
  • Zip codes — which includes socioeconomic status, climate conditions and air quality — had a "far weaker effect" on most diseases than genes and shared environment, Lakhani says. However, it is a potent factor in morbid obesity, he says, although genetics plays a role there as well. Climate also plays a role in flu and Lyme disease, they found.
  • Health care costs: Nearly 60% of monthly health spending can be predicted by analyzing genetic and environmental factors, they found.

Of note: The researchers examined data from newborns to 24 years of age, so the study doesn't analyze diseases that tend to begin later in life.

Outside perspective: Andrey Rzhetsky, a professor of medicine and human genetics at the University of Chicago, says, "Overall, the data are fantastic (very large sample) and technology is solid. ... Yes, there is some inherent ambiguity in [the] attribution of effects to shared genetics vs. shared environment. This can be resolved only with new, higher-resolution data."

"The most important message is that heritability estimates obtained from very different data types appear to agree rather well," Rzhetsky tells Axios.

Go deeper: The full study findings are here.

Go deeper

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