Of course there is no doubt that some diseases, like Huntington’s chorea, beta thalassemia, and cystic fibrosis, can be blamed entirely on one faulty gene. But single-gene disorders affect less than 2 percent of the population; the vast majority of people come into this world with genes that should enable them to live a happy and healthy life. The diseases that are today’s scourges—diabetes, heart disease, and cancer—short circuit a happy and healthy life. These diseases, however, are not the result of a single gene, but of complex interactions among multiple genes and environmental factors.
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