Chromosome Caps Predict Life Span in Birds

Those palm readers predicting your age from your lifeline are making it up. But now scientists say they have found a true lifeline in the cells of Zebra finches. The birds with the longest telomeres—the protective caps at the ends of chromosomes—live the longest, according to a new study. "It is the first time this has been shown for any species," says María Blasco, a telomere researcher at the Spanish National Cancer Research Centre in Madrid, who was not involved in the work.

Telomeres are repetitive DNA sequences that, together with some proteins, sit at the ends of chromosomes to keep them from fraying. They have long been known to shorten with age, and when they reach a critical length, cells stop dividing. While abnormally short telomeres have been implicated in some diseases, studies investigating whether longer telomeres lead to a longer life have shown mixed results.

Now biologist Pat Monaghan and her colleagues at the University of Glasgow in the United Kingdom have come up with the best evidence yet that telomere length correlates with life span. The scientists measured telomere length in red blood cells of 99 captive zebra finches (Taeniopygia guttata). The birds resemble long-lived animals in that there is little restoration of telomeres in body cells as they age. The first measurement was taken at 25 days; the researchers then followed the birds over their natural life span, ranging from less than a year to nearly 9 years, and measured telomeres again at various time points. They found a highly significant correlation between telomere length at 25 days and life span; birds with longer telomeres lived longer. Length measured at 1 year also predicted life span, but the relationship was weaker, whereas at later time points (after 3, 4, 6, and 7 years) there was no correlation, the team reports online today in the Proceedings of the National Academy of Sciences.

This might explain why previous results in humans and animals have not been consistent. "So far studies just looked at individuals that were already quite old," Monaghan says. "But if you look at telomeres in old age, then those individuals with the shortest telomeres will have already died."

"It will be extremely important to get this kind of information for humans," says Blasco, who has co-founded Life Length, a company that already offers patients a test to determine the length of their telomeres. But Monaghan is critical of any attempt to predict an individual's longevity based on telomeres. Some finches with the same telomere length still have different life spans she explains—and the same would probably hold true in humans. "So can I measure telomere length and predict how long someone will live? No, I might be the lucky person who has short telomeres but lives longer."

Cellular gerontologist Thomas von Zglinicki, who studies aging at Newcastle University in the United Kingdom, thinks the researchers' argument, that telomere length needs to be measured early in life, cannot be extended to humans at all. He notes that almost 50% of the birds died before they had reached half the average life span, whereas in humans or mice, usually less than 10% of the population dies so young. Thus, birds with shorter telomeres might simply have been more susceptible to certain diseases, he cautions. "It is possible that the early telomere length in birds predicts the susceptibility for certain diseases and not their natural life span."