As scientists close in on ways to create embryonic stem cell lines without destroying human embryos (see main article, right), some groups are turning to discarded embryos that carry genes for certain diseases.

Sydney IVF, an Australian in vitro fertilization clinic and cell line provider, screens embryos before they are implanted for more than 100 diseases caused by mutations in a single gene or by chromosomal translocations.

We are still the only people in the world doing this with any kind of regularity. Robert Jansen, Sydney IVF

After a successful birth, clients can choose to allow the rejected embryos to be used for research purposes. Since it began its preimplantation genetic diagnosis program in 1997, the company has established a bank of nearly 2,000 embryos that will allow researchers to investigate single-gene diseases such as Huntington's.

The company uses a variation on the standard approach to genetic screening.

Most clinics remove one or two cells from an embryo at the eight-cell stage, which some scientists say could damage the embryo. Sydney IVF scientists instead take samples from the trophectoderm, the outer part of the embryo which will go on to form the placenta, when the embryo has grown to have more than 100 cells. “We are still the only people in the world doing this with any kind of regularity,” says Robert Jansen, the company's managing director.

The researchers hope to differentiate embryonic stem cells developed in this way into particular tissues to help model single-gene diseases and screen potential therapies.

Other scientists, including Yuri Verlinsky of Chicago's Reproductive Genetics Institute, have also said they have developed stem cell lines carrying disease genes from rejected embryos (Nature 429, 691; 2004).

Although the field is still in its infancy, the approach has merit, says John Rasko, head of the Gene & Stem Cell Therapy Program at The University of Sydney's Centenary Institute. “It promises the use of relevant phenotypically defined cells rather than applying normal cells or whole animal models in large-scale screening programs,” Rasko says.

Sydney IVF has an AUS$2.7 million (about US$2.3 million) grant from the government to develop its approach, with the condition that its research will not involve so-called therapeutic cloning, or somatic cell nuclear transfer.

The Australian Parliament endorsed therapeutic cloning for research purposes only late last year, and state legislatures are now debating complementary laws. In early June, the government finalized guidelines for research licenses. The first of those licenses are likely to be granted before the end of the year.