ERRORS have occurred in a type of stem cell that could be used instead of embryonic stem cells – and in tissues made from them.

Joseph Ecker of the Salk Institute in La Jolla, California, and colleagues found genes inappropriately switched on and off in parts of the chromosomes of induced pluripotent stem cells. iPSCs are adult cells reprogrammed to become every type of tissue.

Most mistakes were made either where chromosome arms cross or in their tips, in both iPSCs and tissues made from them. Ecker found no errors in embryonic stem cells, but they raise ethical issues since embryos are destroyed to make ESCs (Nature, DOI: 10.1038/nature09798).

“It’s premature to abandon ESCs until we understand what’s going on with iPSCs,” says Robert Lanza, chief scientist at Advanced Cell Technology in Massachusetts.