Unlocked: How heredity, environment affect gene expression

Everyone has the same set of genes and it is difficult to determine which genes are heritable or controlled by your DNA versus those that may be affected by the environment. Now, no more.

In a path-breaking research, researchers have taken the first steps toward creating a roadmap that may help scientists narrow down the genetic cause of numerous diseases.

The work also sheds new light on how heredity and environment can affect gene expression.

"Teasing out the difference between heredity and environment is key to narrowing the field when you are looking for a genetic relationship to a particular disease," explained Fred Wright, a professor of statistics and biological sciences at North Carolina State University.

Pinpointing the genetic causes of common diseases is not easy as multiple genes may be involved with a disease.

Moreover, disease-causing variants in DNA often do not act directly, but by activating nearby genes.

Wright along with Patrick Sullivan from UNC-Chapel Hill analysed blood sample data from 2,752 adult twins (both identical and fraternal) and an additional 1,895 participants from the Netherlands Study of Depression and Anxiety.

For all 20,000 individual genes, they determined whether those genes were heritable - controlled by the DNA 'dimmer switch' - or largely affected by environment.

A 'dimmer switch' means thst some people may have a particular gene turned all the way up, while others have it only turned halfway on, completely off, or somewhere in between.

Identical twins have identical DNA so if a gene is heritable, its expression will be more similar in identical twins than in fraternal twins.

"This process allowed us to create a database of heritable genes which we could then compare with genes that have been implicated in disease risk," Wright said.

"We saw that heritable genes are more likely to be associated with disease - something that can help other researchers determine which genes to focus on in future studies, Sullivan added.

The study, that appeared in the journal Nature Genetics, is by far the largest twin study of gene expression ever published, enabling researchers to make a roadmap of genes versus environment.