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Gene Environment Interaction
Virtually all-human diseases result from the interaction of genetic
susceptibility factors and modifiable environmental factors, broadly defined to include
infectious, chemical, physical, nutritional, and behavioral factors.
This is perhaps the most important fact in understanding the role
of genetics and environment in the development of disease. Many people tend to
classify the cause of disease as either genetic or environmental. Indeed,
some rare diseases, such as Huntington or Tay Sachs disease, may be the
result of a deficiency of a single gene product, but these diseases represent a
very small proportion of all human disease. Common diseases, such as diabetes
or cancer, are a result of the complex interplay of genetic and environmental
factors.
Genetic Variations
Variations in genetic makeup are associated with almost all disease.
Even so-called single-gene disorders actually develop from the
interaction of both genetic and environmental factors. For example,
phenylketonuria (PKU) results from a genetic variant that leads to deficient metabolism
of the amino acid phenylalanine; in the presence of normal protein intake,
phenylalanine accumulates and is neurotoxic. PKU occurs only when both the
genetic variant (phenylalanine hydoxylase deficiency) and the environmental
exposure (dietary phenylalanine)
are present.
Environmental
Factors
Genetic variations do not cause disease but rather influence a
person’s susceptibility to environmental factors. We do not inherit a disease state per se. Instead, we inherit a set
of a susceptibility factors to certain effects of environmental factors and therefore
inherit a higher risk for certain diseases. This concept also explains why
individuals are differently affected by the same environmental factors. For
example, some health conscious individuals with “acceptable” cholesterol
levels suffer myocardial infarction at age 40. Others individuals seem immune to heart
disease in spite of smoking, poor diet, and obesity. Genetic variations
account, at least in part, for this difference in response to the same environmental
factors.
Intervention
Strategies
Genetic information can be used to target interventions.
We all carry genetic variants that increase our susceptibility to
some diseases. By identifying and characterizing gene-environment interactions, we
have more opportunities to effectively target intervention strategies.
Many of the genetic risk factors for diseases have not been identified, and the
complex interaction of genes with other genes and genes with environmental
factors is not yet understood. Clinical and epidemiological studies are
necessary to further describe these factors and their interactions. However, as
our understanding of genetic variations increases, so should our knowledge of environmental factors, so that ultimately, genetic information can
be used to plan
appropriate intervention strategies for high-risk individuals. |
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