Researchers at the University of Virginia and elsewhere have discovered there are tens of thousands of previously unknown "microDNAs" outside the chromosomes in our cells. The groundbreaking research suggests that the generation of these microDNAs may create an unexpected genetic variation in tissue cells. That variation, in turn, may contribute to diseases that are suspected to have a genetic predisposition, but for which there are no suspect genes, such as autism.

The research, led by Dr. Anindya Dutta, Harry F. Byrd Professor and chair of Biochemistry and Molecular Genetics at the U.Va. School of Medicine, upends the commonly accepted notion that DNA is wholly contained within long chromosomes. Dutta's team detected the short, circular microDNAs in both mouse and human cell lines, shedding new light on the makeup of mammalian DNA.

The team determined that the generation of microDNAs leads to genetic variation within cells of the same tissue. Mistakes made as the DNA-copying machinery does its work prompt "micro-deletions" as the faulty microDNA is removed. This creates a mosaic of genetically varied cells within the same tissue, possibly leading to functional differences among them. Because of the nature of the process, there is an element of chance in which genes will be intact and which will suffer micro-deletions, Dutta said.

"The resulting genetic variation in our tissues could be important for diseases like schizophrenia or autism that have a genetic predisposition, but for which a single gene with a causative mutation has not yet been found," he said.

In addition, the findings may help explain genetic behavior in plants that appears to defy the laws of genetics put forth by Gregor Mendel, the 19th-century Austrian known as "the father of genetics."

The new research findings have been published online in the journal Science. The team includes researchers at U.Va. and the University of North Carolina at Chapel Hill.