The Inheritance of Disease
A Paradigm for the Inheritance
We have learned a great deal about the heritability of various diseases in the last decade or two. Many of the major disease killers in the United States, including heart disease, cancer, stroke, diabetes, and atherosclerosis, are known to have strong genetic components, and the genetic basis of these diseases is now reasonably well understood. Perhaps the greatest increase in knowledge over the last decade has concerned the heritable nature of cancer.6 We now know unequivocally that individuals in certain families have an elevated risk of cancer because they have inherited a genetic susceptibility to the disease. But the idea that individuals can also inherit a susceptibility to certain behaviors still seems heretical to many. Nevertheless, inheritance of disease seems to mirror the inheritance of behavior in many instructive ways; the lessons learned from studying disease inheritance even suggest several strategies for studying human behavior.
It is far easier to study the heritability of disease than to study the heritability of behavior, because disease is overt and usually easy to characterize. If a patient has cancer, that patient is generally quite ill, and the illness can usually be unambiguously diagnosed by a physician. Certain measurable features of the illness are present: the tumor can be visualized by magnetic resonance imaging (MRI) or by X-ray; the dimensions of the tumor can be measured; the blood chemistry can be analyzed; the presence of tumor antigens can be characterized; the growth rate of the tumor can be estimated; the genetic features of the tumor can be defined; or the clinical status of the patient can be