A growing body of research on these "epigenetic" changes are leading geneticists to rethink the conventional view that all human disease is fundamentally tied to DNA sequence variation (changes in the actual sequence of the DNA nucleic acid code of A's, C's, G's and T's within any given gene).

The DNA within human cells contains the information for roughly 35,000 different proteins that carry out the body's functions. But not all of these genes are active all of the time. Like switches, epigenetic modifications to proteins surrounding the DNA regulate a given gene's activity, such that only those that are required in a particular cell are active (switched on). These changes constitute a "memory" of gene activity that can be passed on each time a cell divides.

If these epigenetic modifications do not occur properly, the result can cause some genes to become switched on or off incorrectly, thereby having profound biological consequences. Incorrect epigenetic modifications have been implicated in many human disorders including several types of cancer, birth defects and mental retardation.

"These expression changes are heritable and are not related to sequence changes in the gene that is directly affected", said Dr. Terry Magnuson, Kenan professor of genetics and director of the Carolina Center for Genome Sciences. "Sequencing the human genome will not necessarily lead one to discover why these genes are expressed abnormally."

For example, there is a recent awareness among scientists of a new type of health threat posed by environmental chemicals that can disrupt endocrine signals during critical periods of development through epigenetic alterations. Additionally, researchers studying
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Contact: Leslie Lang
llang@med.unc.edu
919-843-9687
University of North Carolina School of Medicine
9-Mar-2003