Autoimmune Thyroid Disease

An Unfortunate and Lengthy Adventure in Misdiagnosis

Homozygosity – not always a bad thing

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Marry your cousin to have long-lived kids? Inbreeding is not usually mooted as the key to longevity, but Giuseppe Passarino of the University of Calabria in Rende, Italy, thinks it might be. “Everyone knows that inbreeding is bad – it increases your chances of catching a range of diseases,” he says. “But on the other hand, our study suggests that if inbreds don’t get those diseases when they’re young, they might have a better chance of long life.”

Passarino and his colleagues used census data to identify a geographically isolated region of southern Italy with more than its fair share of male nonagerians. When the team looked at the local phone book, they found many people in the region shared the same surname, suggesting marriage between related individuals was common (Annals of Human Genetics, DOI: 10.1111/j.1469-1809.2007.00405.x).

“The level of inbreeding can be measured quite precisely by studying surname distribution,” says Passarino. Because a surname is passed through the paternal line, it behaves like a gene transmitted through the Y chromosome, he says.

Everyone has two copies of each gene. In a large gene pool there is a high chance that those copies will be distinct. But in a small, inbred community, the gene pool remains the same and it is more likely that an individual will be “homozygous” – with two identical copies of a gene.

“Longevity seems to be linked to homozygosity,” Passarino says. This may be because certain copies of some genes boost lifespan, and carrying two of them doubles the effect. A number of DNA analyses have located regions of the genome where centenarians show an unusually high level of homozygosity, he says.

“It is theoretically possible to observe more centenarians as a result of inbreeding,” says Leonid Gavrilov at the University of Chicago, but he wonders why only men were the beneficiaries.

Passarino says it may be because the genetic component of longevity plays a more important role in men, whereas in women, environmental factors come to the fore. Healthcare has improved in western Europe over the past 60 years, which has benefited women more than men. For example, in Denmark the number of male centenarians is 10 times as high because of better healthcare, but the number of females is 50 times higher, he says. The region that Passarino identified is economically poor and has limited healthcare. This could explain why fewer women than men live to old age there.

Bruce Carnes of the University of Oklahoma cautions against marrying a relative, however. “Homozygosity is typically a very bad thing,” he says. “Almost every discussion of inbreeding that I have ever read has emphasised its downside.” Inbred humans live to a ripe old age

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Written by alienrobotgirl

26 January, 2008 at 7:52 pm

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