"Nature versus nurture" and incompletely penetrant mutations

Abstract

Lessons from twin studies of parkinson's disease The debate over the relative roles of “nature versus nurture” remains unresolved in many fields of study, from childhood education to animal behaviour or neurodegenerative disorders. Points of view frequently are polarised, either nature or nurture, rather then exploring the ways in which both sides play critical and complementary roles. Proponents of “nature” argue that human attributes are uniquely and primarily conditioned by genetics, opposing the view of those who think that environmental influences and experience determine individual differences. Arguments similar to those brought to bear regarding acquisition of skills, language, or cognitive styles also apply to human pathology. Often, in the discussion of disease the terms used are “genetic” versus “environmental”, but the implication is the same as in the “nature” versus “nurture” debate. Disorders considered to be primarily genetic are ones in which the presence or absence of genetic mutations is the primary determinant of disease, independent of environmental circumstances. A disease considered to be primarily environmental is one in which people of virtually any genetic background can develop the disease provided that they are exposed to the necessary environmental factor or factors. However, for many disorders, the risk is strongly influenced by both genetic and environmental factors.1, 2 For example, a susceptibility gene may strongly influence the risk of developing a disease only in response to a specific environmental exposure. If the environmental exposure occurs infrequently, the gene will be of low penetrance, and it may seem that the environmental exposure is the primary determinant of the disease, even though the gene is required for developing the disease. Therefore, even when environmental agents are suspected to be a major cause of a particular disease, this does not exclude the possibility that genetic factors also play a major part, particularly …