"Jumping genes" make each person unique: study

WASHINGTON (Reuters) - Stretches of DNA known as "jumping" genes are far more common than anyone thought, and almost everyone has a unique pattern of them, U.S. researchers reported on Thursday.

They also found an unexpectedly high number of these jumping genes, known as transposons, in lung tumors and said they may hold clues to the highly deadly cancer.

"We found that if you have a child, the child could have one or more new copies of these transposons that you don't have," Scott Devine of the University of Maryland School of Medicine said in a statement.

"From these findings, we predict that there is going to be more variation in human genomes than scientists first believed," added Devine, who led the research while at Emory University in Atlanta.

The findings could help fuel a revolution that scientists hope will lead to tailored medicine and far more targeted use of drugs and other therapies to treat and prevent disease.

Transposons are sequences in the DNA code that can replicate themselves. They "jump" from one place to another on the chromosomes. Devine's team found unique transposons in more than 90 percent of the 76 people they studied, they reported in the journal Cell.

These mutations can affect the functions of other genes. Stretches of DNA right in front of or behind a gene can turn it on, turn it off, or affect the way it functions.

That people have transposons is not new. "Forty-five percent of the genome is known to be transposon sequences," Devine said. But most hopped in and are now inactive, passing down unchanged and in place from one generation to the next.

"What we are interested in are the ones that are moving around today. We found an average of 15 new insertions per person," Devine said in a telephone interview.

CHEAPER NEW TECHNOLOGY

New genetic sequencing technology made it possible to find these transposons. It costs thousands of dollars to map an individual's genome, the entire genetic sequence, but companies such as Illumina, Life Technologies, Roche and others are driving the price down.

Devine's team used Roche's 454 sequencer to find 1,145 new inserted transposons that had not been documented before.

They developed a genetic probe that would target only these active jumping genes and estimated a new insertion is happening with each generation.

The human genome has 3 billion so-called base pairs -- the A, C, T and G of the genetic code. "This could affect every base pair somewhere on the planet," Devine said.

"What is that doing to people? You could imagine that doing a lot of things, causing diseases."

Each person has the same basic 20,000 genes, but each gene is made up of many base pairs and there are subtle changes unique to everyone. In addition, DNA outside the genes affects the body in ways that are only beginning to be understood.

The transposons jump into these non-coding regions, but also sometimes into the genes.

"If you think of the human genome as a manual to build a complex machine like an aircraft, imagine what would happen if you copied the page that describes passenger seats and inserted it into the section that describes jet engines," Devine said.

When they looked at brain and lung tumors, Devine's team found transposons seem to be especially busy in lung cancer but not brain cancer. One of the many next steps will be to understand why this is.

(Editing by Xavier Briand)