The Important 0.1 Percent

(Nineteenth in a series of topical blogs based on chapter by chapter excerpts from Opiate Nation. Translation into most languages is available to the right.)

DNA sequences for any human is approximately 99.9 percent identical to every other human. That means that only 0.1 percent of our genetic makeup is unique to us. Genes are functional units of DNA that make up the human genome. But don’t be fooled into thinking that 0.1 percent variation is insignificant. It is nearly 3 billion base pairs of DNA which boils down to 3 million differences that determine our physical features like hair and eye color and health risks or protection from diseases such as heart disease, diabetes – and addiction. Genes influence the numbers and types of receptors in peoples’ brains, how quickly their bodies metabolize drugs, and how well they respond to different medications.

The National Institute of Drug Abuse (NIDA) reports that family studies that include identical twins, fraternal twins, adoptees, and siblings suggest that as much as half of a person’s risk of becoming addicted to nicotine, alcohol, or other drugs depends on his or her genetic makeup. Scientists estimate that genes – including the effects environmental factors have on a person’s gene expression, called epigenetics – account for between 40 and 60 percent of a person’s risk of addiction.

Epigenetics – epi meaning “above” – is the study of functional, and sometimes inherited, changes in the regulation of gene activity and expression that are not dependent on gene sequence. This means exposures or choices people make can actually “mark” (remodel) the structure of DNA at the cell level. So epigenetic regulatory systems enable the development of different cell types (e.g., skin, liver, or nerve cells) in response to the environment. These epigenetic marks can affect health and even the expression of the traits passed to children. For example, when a person uses cocaine, it can “mark” the DNA, increasing the production of proteins common in addiction which is believed to correspond with drug-seeking behaviors.

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