40 percent of diseases are influenced by genetics, new study finds

The nature versus nurture debate remains one of the longest-running discussions among the scientific community.

It can be a complicated task to determine whether it is genetics or environment that is more influential on development, disease, and behavior. But now, a new study conducted by researchers from Harvard University and the University of Queensland in Australia used a massive insurance database to help shed insight on the age-old question.

Studying twins, both fraternal and identical, is one the best ways to study the influence of genetics versus environmental factors because twins have similar DNA. Identical twins have matching DNA.

However, twin nature versus nurture studies usually tackle one disease at a time or have a small sample size as finding twins that meet the right study parameters can be difficult.

This recent study is the largest twin study of its kind, and the researchers analyzed data from an insurance database of nearly 45 million people in the United States.

The researchers were able to examine the genetic and environmental effects on 560 different diseases and health conditions for 56,396 pairs of twins and 724,513 siblings. The study was published in the journal Nature Genetics.

“The nurture-versus-nature question is very much at the heart of our study,” Chirag Patel, the senior author of the study, told the Harvard Gazette. “We foresee the value of this type of large-scale analysis will be in shining light on the relative contribution of genes versus shared environment in a multitude of diseases.”

One of the largest challenges that come with understanding genetic influence compared to environmental influence on diseases is that it is not so neatly black and white. Diseases are rarely purely environmental or genetic, and instead, a complex combination of certain environmental factors and genetics create a perfect storm of sorts.

By using such a large dataset, the researchers were able to overcome many of the challenges that arise when studying the interplay between genetics and environmental factors.

Each pair of twins had been part of the insurance database for three years or more, and the researchers had data on pairs of twins starting with newborns to age 24.

The researchers used a statistical approach to estimate how many pairs of twins were fraternal and how many were identical. The data included a wide range of genetic and environmental factors including pollution, climate conditions, socioeconomic status and clinical diagnoses, red and white blood cell counts, and cholesterol levels.

After analyzing the data and accounting for all these different variables, the researchers were able to identify which diseases were more strongly influenced by genetics among the twins and which were due to certain environmental changes.

225 out of 560 of the diseases studied, roughly 40 percent, were linked to genetics, and 138 were influenced heavily by environmental factors because the twins shared households and social settings.

Eye disorders had little to do with genetics and 27 out of 42 eye diseases were linked to strong environmental influences. Cognitive disorders and reproductive problems had the strongest genetic influences.

145 of the diseases studied related to socioeconomic status, and the morbid obesity was heavily linked to status, but the researchers found that climate, status, and air quality did not have as strong an impact on disease as a shared household environment.

The researchers hope that their study will help future studies narrow down the genetic and environmental influence on diseases.

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By Kay Vandette, Earth.com Staff Writer