A new study conducted by scientists at the Centre for Addiction and Mental Health (CAMH) suggests that DNA may not be the only carrier of heritable information, and that a secondary molecular mechanism called epigenetics may also account for some inherited traits and diseases.
The researchers say that their findings challenge the fundamental principles of genetics and inheritance, and potentially provide a new insight into the primary causes of human diseases.
A trait or disease is called heritable if genetically identical twins are more similar to each other than genetically different twins.
In molecular terms, heritability has traditionally been attributed to variations in the DNA sequence.
Dr. Art Petronis, head of the Krembil Family Epigenetics Laboratory at the CAMH, conducted a comprehensive epigenetic analysis of 100 sets of genetically identical and genetically different twins in the first study of its kind.
"We investigated molecules that attach to DNA and regulate various gene activities. These DNA modifications are called epigenetic factors," said the lead researcher.
His study demonstrated that epigenetic factors - acting independently from DNA - were more similar in identical twins than their non-identical counterparts, suggesting that there was a secondary molecular mechanism of heredity.
The epigenetic heritability might help explain currently unclear issues in human disease, such as the presence of a disease in only one identical twin, the different susceptibility of males (e.g. to autism) and females (e.g. to lupus), significant fluctuations in the course of a disease (e.g. bipolar disorder, inflammatory bowel disease, multiple sclerosis), among numerous others.
"Traditionally, it has been assumed that only the DNA sequence can account for the capability of normal traits and diseases to be inherited," says Dr. Petronis.
"Over the last several decades, there has been an enormous effort to identify specific DNA sequence changes predisposing people to psychiatric, neurodegenerative, malignant, metabolic, and autoimmune diseases, but with only moderate success. Our findings represent a new way to look for the molecular cause of disease, and eventually may lead to improved diagnostics and treatment," the researcher added.
The study has been published in the online edition of the journal Nature Genetics.