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"Go not gentle into that good night."(7/23/03)
At the end of your chromosomes, there is a sequence of repetitive DNA that doesn't 'do' anything in the traditional sense of the word. These 'end caps' are called telomeres. Because of the way DNA reproduces itself, with each copy that's made (such as when cells divide to grow) a bit more of these telomere 'end caps' are lost. This matters, because when the protective telomeres run out, coding DNA (actual genes) start to be damaged. At this point, the cells become semi-dormant: They have difficulty functioning and dividing, and the organism ages and dies.
Telomere loss isn't the only cause of aging, but it seems to represent a sort of 'death clock' in humans; each cell can only divide so many times. In human egg and sperm cells, an enzyme called telomerase re-builds the telomeres, preventing the new generation of offspring from being born with shortened lifespans.
Cancer cells usually have mutations that activate the telomerase gene, allowing them to grow and divide indefinitely; a tumor cell is virtually immortal.
What's that got to do with the price of tea in China? Consider a hypothetical experiment: An egg is fertilized in-vitro (literally, "in glass", such as a petri dish) at one of the reproductive medicine hospitals. Then, before the embryo is implanted into the mother-to-be, a large dose of the telomerase enzyme is injected into it. As the embryo grows and divides, the macrodose of telomerase enzymes extend the prospective person's telomeres...double...triple...tenfold.
And so...we watch the child grow. With a little luck, they'll develop normally, unaware of and not visibly affected by this strange manipulation of their chromosomes. They turn ten. Twenty. Thirty. Forty. Something isn't quite right: The now-adult isn't aging. They've reached the point where their body should be running down, skin starting to wrinkle and muscle density declining as cells start to reach the genetic time limit on their ability to reproduce; to heal damage and grow. But the slightly engineered human isn't aging; their telomeres are still far longer than those of the average newborn. Another decade...and another. A hundred years pass, and the patient still looks an indeterminate thirty-something. His heart is strong, his skin elastic, muscles firm; the legions of cells that should have given up by now are still fighting to live, to repair and rejuvenate tissues the way they do when we are young. The patient eventually dies at the age of 248 in a sky-diving accident, still in decent medical shape. We won the gamble.
Roll the dice again. The patient seems unaffected. Old age comes, right on schedule, bearing the thousand indignities of prostate exams, arthritis, failing memory...and finally a natural death at the age of 84. We missunderstood the role of telomeres in aging.
Roll the dice again. The child grows. At the age of sixteen, tumors begin to appear. Treatment proves futile; his extended telomeres have granted long life to polyps and cellular growths that might otherwise have quickly ran themselves out of steam as they reached the telomere-enforced limited on cellular divisions. The patient dies in terrible pain, riddled with cancer, at the age of 24. We underestimated the role of telomeres in controlling tumor growth.
This experiment can be done today. All the technology is off-the-shelf. And so I offer it as a specific case of a broader philosophical question: What do you want...and how much are you willing to risk for it?
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"Eagle may soar, but gopher never get sucked into 747 engine." -ancient Native American saying.