Individual Variability

Biological Factors that Underlie Individual Susceptibility to Environmental Stressors and Their Implications for Decision-Making

April 18-19, 2012

The National Academies
Keck Center
500 Fifth St. NW
Washington, DC 20001
View Map


It is well known that there is a range of human susceptibility to effects of given environmental exposures. This range is due in part to endogenous factors such as genetics and epigenetics, physiology, lifestage, and other biological differences. Variability in individual exposures also contributes significantly to variability in human susceptibility, but this meeting focuses on the endogenous/biological factors.

The 2010 National Research Council report Science and Decisions: Advancing Risk Assessment notes that it is difficult to estimate an average population risk without understanding how the risk varies among individuals in the population. However, the default approach in risk assessment to account for individual variability is to assume that a ten-fold decrease in allowable exposure will protect the most sensitive subpopulations, even though seldom it is known whether such approach may be overprotective or insufficient.

Emerging molecular techniques, such as next generation sequencing, are advancing scientists’ ability to characterize how individuals differ inherently (genetically and otherwise). Such information can also be used to predict how such individual differences may affect one’s susceptibility to a given exposure.   While it may not be feasible to determine susceptibility of each individual to each potential exposure, clearly we can characterize the range and a distribution of biological variability in humans at a more granular level than assuming a ten-fold uncertainty factor.

This meeting explored new and innovative approaches to characterizing individual variability arising from endogenous, biological factors and its impact on susceptibility to risks from environmental exposures. Discussions also delved into how to bring new data collection and analytic approaches to bear and layer them with conventional data on variability.  Topics spanned a range of approaches, from molecular analyses to the use of human cells and animal models as experimental systems, and how these approaches can be used to better characterize individual variability linked to endogenous factors in toxicity, epidemiology. and genome-wide-association studies.

This meeting also considered the implications of emerging approaches to policies designed to address susceptibility in public health and risk assessment. Meeting participants addressed approaches for and challenges to describing the relationships among individual variability, disease susceptibility, and public health.