In a recent study, researchers compared DNA of identical twins of different ages. They showed that structural modifications of DNA, where segments change direction, are duplicated or completely lost, are more common in older people. The results may help explain why the immune system weakens with age. The scientists examined normal blood cells from identical twins. The results showed that large rearrangements were only present in the group older than 60 years old. Rearrangements were also found in the younger group. The changes were smaller and less complex, but the researchers also showed that the number of rearrangements correlated with age. “We were surprised to find that as many as 3.5 percent of healthy individuals older than 60 years carry such large genetic alterations. We believe that what we see today is only the tip of the iceberg and that this type of acquired genetic variation might be much more common,” says Jan Dumanski, one of the authors of the paper.