By sequencing more human genomes more thoroughly than ever before, researchers have shown that most of the genetic variation in the human population is due to rare variants. These rare versions of genes are more likely to affect human health than are their common counterparts — which could make it more difficult to link gene variants to disease than previously thought.

Joshua Akey and Michael Bamshad at the University of Washington, Seattle, and their colleagues sequenced 15,585 genes in 2,440 people. The researchers found that 86% of the gene variants that they detected were rare, as were more than 95% of variants that were predicted to have a medical or biological effect.

Meanwhile, a team including Matthew Nelson at GlaxoSmithKline in Research Triangle Park, North Carolina, and John Novembre at the University of California, Los Angeles, report that more than 74% of variants identified by sequencing 202 genes in 14,002 people were carried by only one or two of the individuals.

Andy Clark and Alon Keinan of Cornell University in Ithaca, New York, used data from previous sequencing studies to show that rapid growth of the human population, starting 1,400 years ago, helped to seed the human genome with numerous rare variants.

Science;; 336, 740–743 (2012)

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