This past spring Woo Suk Hwang of Seoul National University in South Korea and his colleagues reported stem cell work in which they inserted DNA from skin cells into donated eggs. Some of the fused eggs grew to form blastocysts, an early stage of development from which the researchers harvested stem cells. The small study also highlights in a novel way how the quality of eggs declines with age.

Number of egg donors:

Younger than age 30: 10

Older than age 30: 8

Percent of eggs fused with DNA that developed into blastocysts from donors:

Under 30: 24.4

Over 30: 23.1

Percent of blastocysts that yielded stem cells from donors:

Under 30: 40.9

Over 30: 22.2

Percent of stem cell lines established from oocytes from donors:

Under 30: 7.2

Over 30: 3.3

SOURCE: Science, June 17