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INTRODUCTION

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Social policies, public health, and medicine, in that general descending order of importance, have improved human well-being and longevity in the twentieth century. Yet disease continues, in the form of sick populations and sick individuals,1 and unhealthy longevity is a macroeconomic problem.2 Naturally, there has been a response—one composed of social policies, public health, and medicine. In Canada, a major milestone in this response was the government document A New Perspective on the Health of Canadians,3 which outlined the Health Field Concept. Reasonable, thoughtful, and provocative, this document espoused a four-pronged attack on disease, and it welded ideas on lifestyle, environment, health care organization, and human biology into an approach to address disease more effectively. Considerable attention has been paid to the first three but rather less has been heard about the fourth component, namely, the biological basis of disease. This chapter addresses that particular theme. Our topic is genetic determinants of disease and examples of genetics and genetic disease in public health as illustrated by newborn and prenatal screening programs.

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At least 5.3% of liveborn individuals in a large population of over a million consecutive births were found to have diseases with an important genetic component before age 25 years.4 If congenital anomalies (some of which have a genetic cause) are also included, then 7.9% of the population has been identified by age 25 as having a genetic disorder. A sampling of over 12,000 admissions to a pediatric hospital found that 11.1% were “genetic,” 18.5% were for congenital malformations, and 2% were “probably” genetic.5 These findings have been confirmed in other studies.6,7

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Health is a state of homeostasis, and it is maintained in the face of a changing and shifting environment. The central tendencies of metrical traits (mean values) are the quantitative measures of homeostasis (e.g., level of blood glucose, cholesterol, phosphorus, osmolarity, blood pressure, and so on).8 The polypeptide mediators of homeostasis (enzymes, transporters, channels, receptors, etc.) that are essential to this process of homeostasis are encoded by genes, descended to homo sapiens through the evolutionary process. Individuals retain health if experience does not overwhelm homeostasis or mutation does not undermine it.

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In the conventional medical model, disease manifestations (symptoms and signs) are the product of a process (pathogenesis) that has an origin (cause). The manifestations of disease dominate the practice of medicine. Consideration of cause, incidence, and distribution of cases constitutes the public health focus. Public health in genetics takes this a step further, by identifying and treating genetic disorders in large, universal populations of newborns, or providing earlier detection of birth defects in pregnant women.

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Rather than thinking of the determinants of disease as outside ourselves, our genetic individuality should be seen as a potential ingredient in the origin of health. Because each individual has a different risk for disease, progress will be optimized if this ...

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