The research team, lead by University of Alabama at Birmingham scientists, found subtle differences in twin's DNA that may lead to better understanding of genetic diseases, the university said Friday in a release.

The findings are published online in the American Journal of Human Genetics.

The researchers studied 19 pairs of identical twins and found differences in copy number variation in DNA. Copy number variation (CNV) occurs when a set of coding letters in DNA is missing, or when extra copies of segments of DNA are produced.

"The presumption has always been that identical twins are identical down to their DNA," said lead authors Carl Bruder and Jan Dumanski of UAB's Department of Genetics. "That's mostly true, but our findings suggest that there are small, subtle differences due to CNV."

The researchers said the information could result in quicker diagnosis for genetic disorders.