Dr. Spelsberg said the knowledge produced by these emerging fields will enable physicians to customize diagnosis and treatment based on each patient’s genetic endowment. Already, researchers have identified about 10 “obesogenes” involved in the maintenance of body weight. Dr. Spelsberg displayed a photo of two rats side by side. One appeared normal, while the other was enormously fat. The fat mouse, he explained, lacked the gene for leptin, the hormone that triggers a feeling of satiety.
But the genes themselves are only part of the story. Genes also mutate or “morph” into polymorphisms that can leave the body more susceptible to dysfunction. Some polymorphisms are inherited, some develop over time. “Identical twins are born with the exact same DNA, but they develop polymorphisms with age and start to look different,” Dr. Spelsberg said. “They grow apart.”
The environment plays a role in developing polymorphisms. “People who live in cities get more polymorphisms,” Dr. Spelsberg said. “They say for every 15 cigarettes you smoke you develop a new polymorphism. Smokers have a lot more polymorphisms compared to nonsmokers. And people who get lots of sun have more polymorphisms in their skin. What they’re finding is that the more polymorphisms you get, the shorter your lifespan will be.”