Monday, June 19, 2006

Pre-implantation Genetic Haplotyping

This article in today's Guardian reports that British scientists have announced an advanced screening test for embryos which uses a form of DNA fingerprinting called pre-implantation genetic haplotyping (PGH). PGH is different from PGD. With PGD the test tries to identify a specific altered gene linked to an inherited illness. But with PGH the the test looks for the more uniform chromosomal DNA fingerprints, or markers, near the gene. Here are some excerpts from the Guardian article:

It takes about two months and has the potential to detect many more disorders than the current standard screening test, known as pre-implantation genetic diagnosis (PGD), which identifies specific mutations in genes.

For example, about 1,000 mutations are thought to cause cystic fibrosis, but only one, the most common, can be identified by PGD.

"We don't have to know the precise details of a mutation, just whereabouts it is in the genome," Professor Peter Braude, who developed the technique at Guy's hospital, said of the new method. "It is more accurate and reliable than PGD and could be available for a whole range of disorders."

....For the test, blood samples are taken from a couple and any affected children or relatives, and DNA from these samples is tested and compared.

Using a technique to create many more copies of chromosomes in the laboratory, scientists look for markers that show if an embryo carries the problem chromosome or a disease-free version.

"You can actually track the gene through the family without looking at the gene. You can see which embryos are affected and which are not," Alison Lashwood from Guy's told Reuters.

The technique is similar to forensic DNA tests, which search for specific short sequences of DNA from a suspect and compare them against patterns in DNA taken from a crime scene.