DNA structure (Image: Michael Ströck via Wikimedia Commons)

Prevailing wisdom holds that every cell in the body contains identical DNA.

But Yale researchers say they examined skin stem cells and found a number of genetic variations in a variety of skin tissue.

The study, published in Nature, could have profound implications for genetic screening.

“We found that humans are made up of a mosaic of cells with different genomes,” said lead author Flora Vaccarino, M.D., from the Yale Child Study Center. “We saw that 30 percent of skin cells harbor copy number variations (CNV), which are segments of DNA that are deleted or duplicated. Previously it was assumed that these variations only occurred in cases of disease, such as cancer. The mosaic that we’ve seen in the skin could also be found in the blood, in the brain, and in other parts of the human body.”

It’s been long believed that all of our cells have the very same DNA sequence.

Other scientists conducting similar genetic research have theorized the DNA sequence of a cell could be modified during the cell’s development – when DNA is copied from a mother cell to a daughter cell.  These many changes to a cell’s original DNA, they say, could affect an entire group of genes.

While it’s difficult for scientists to actually test these theories, the Yale researchers say they have been able to do so for their new study.

To reach their findings, the research team used whole genome sequencing – a genome is a complete set of hereditary information – to study induced pluripotent stem cells (iPS), which are genetically engineered stem cells developed from a mature-differentiated cell.

The team grew cells taken from the inner upper arms of people from two families. For two years, the researchers examined their genetically engineered iPS cell lines, compared them to the original skin cells, and noted any differences between each cell’s DNA.

The team also conducted further experiments to see what might have caused the differences to occur.

While the research in the project outlined in this recent study was limited to finding variations in DNA sequencing within skin cells, the Yale team is continuing its studies to see if these same DNA variations can be found in developing brain cells of animals as well as humans.