One of the big question marks hovering over cloning research is whether the technique has any long-term adverse effects. Now, a new study by Japanese investigators—the first to track cloned mammals from birth to death—has found that mice cloned from somatic cells have a significantly shorter life span than those conceived in the usual way.
Researchers at the National Institute of Infectious Diseases in Tokyo and colleagues examined 12 male mice that had been cloned from immature cells in the testis and compared them with 13 control male mice. Half of the control mice were the product of natural mating; the others were derived from spermatid injection (injecting a sperm nucleus into a recipient egg to mimic the cloning technique).