In an effort to better understand the genetics of cancer, researchers at the Washington University School of Medicine in St. Louis have completely sequenced the genome of a woman fatally afflicted with leukemia, a cancer of the blood. This was an important step because the exact genetic errors that lead to many cancers are not known.
To determine which genes might be involved in this particular form of leukemia, researchers performed a conceptually simple – but technically very challenging – experiment: compare the DNA sequence from the woman's leukemic bone marrow cells to DNA sequence from her own normal skin cells, and look for differences. Ideally, both cell types should have basically identical DNA sequences (all cells contain the same master set of DNA "instructions"). Differences arise, though, because cells acquire DNA mutations (errors) during one's lifetime. Some of these may contribute to disease.
After reading the 3 billion letters of her tumor and skin genomes many times over (~140 billion total letters of DNA sequenced!), they found 10 gene mutations in her marrow cells that likely led to the disease. Eight of these genes had not previously been linked to leukemia.
Exactly how these genes might contribute to leukemia remains to be determined. But researchers now have a new set of targets that may help in the search for better diagnostics and ultimately cures. Sequencing many more genomes of patients with leukemia will be necessary for the full genetic picture to emerge, but this is certainly a great start.
All of this work has been made possible by the completion of the Human Genome Project in 2003, and by amazing technical advances in our ability to sequence DNA.
More about the idea of “personalized medicine” – using genetic information to help determine the best course of health care – can be found in Dr. Rex Chisholm’s recent SiS article. You can also listen to an audio interview with Dr. Timothy Ley, who led the study, courtesy of NPR's Science Friday.