New study explains why identical twins aren't always identical

BOSTON -- A new study helps explain why identical twins aren't always so identical.

Researchers at Washington State University studied identical twins and found that the more physically active siblings had lower signs of metabolic disease such as smaller waist sizes and lower BMIs than their less active siblings.  

Even though identical twins have the same genes, scientists found differences on a molecular level in how genes were expressed. This suggests that markers of metabolic disease are not just baked into our DNA but are strongly influenced by how we interact with our environment.  

They say this difference in genetic expression in identical twins may also help explain why identical twins develop different diseases as they get older.