Gene Activity May Vary in Identical Twins
Which Genes Are Active May Play a Role in Physical Differences in Twins
WebMD News Archive
July 6, 2005 -- Identical twins may share the same DNA, but variations in
which genes are active may lead to some important differences.
A new study shows that differences in physical appearance or disease risk
found in identical twins may be caused by variations in which of the matching
genes are activated.
The results appear in the current edition of Proceedings of the National
Academy of Sciences.
Identical twins are produced from a fertilized egg that has divided in two;
they share identical genetics. Yet not all of these twins appear identical and
disease risk may also differ.
Patterns of Genetic Activity
In the study, researchers looked at the genetic profiles of 80 sets of
identical twins in Spain, who ranged in age from 3 to 74 years old.
Researchers found that in 35% of the twin pairs, individual twins had
significantly different patterns of active genes. The remaining 65% had
identical patterns of genetic activity.
The results showed that while young twins were genetically
indistinguishable, older twins displayed major differences in the content and
distribution of their genetic information, which resulted in unique gene
The study also showed that the greatest differences were seen in twin pairs
who had spent less of their lifetimes together or had different medical
Researchers say the results support the theory that environmental factors,
including smoking, diet, and physical activity may affect a person's gene
activity and explain some of the differences in disease risk found among
The study helps provide insight into the genetic causes of disease risk in
identical twins but may be generalized to nontwins.