Japanese researchers who cloned a dozen mice reported on Sunday that virtually all of the animals died early, a report that casts more doubts on the safety of cloning.
The mice had abnormal livers, lungs and perhaps some immune system anomalies, the team reported.

They also noted that clones may be born
“old.” Some clones have shortened telomeres, which are a kind of cap on the chromosome, the structures that carry the genes. Each time a cell replicates, this telomere cap frays a little and this process is believed to be associated with aging.