The Faulty Gene Behind Chroni... Video Transcript

Participants

, John M. Goldman MD, Peter Nowell MD, Janet D. Rowley MD

Summary

The genetics of chronic myeloid leukemia are now well understood. Listen to researchers as they explain the path they took to their remarkable discoveries beginning over 40 years ago, in a research lab in Philadelphia.

Webcast Transcript

ANNOUNCER: Scientists today know a great deal about chronic myeloid leukemia. The story of their research into the disease goes back 40 years, to a lab in Philadelphia. Peter Nowell at the University of Pennsylvania stumbled on a technique to make the chromosomes of dividing cells visible under the microscope. Nowell showed slides of chromosomes from CML patients to a young graduate student, David Hungerford. Hungerford spotted what appeared to be an abnormally small chromosome in each of the samples.

PETER NOWELL, MD: He spotted a very small chromosome in one type of human leukemia. It was there in essentially every cell, and it was there in essentially every case. So this argued very strongly that this altered abnormal chromosome was playing a role in the development of this tumor.

ANNOUNCER: Nowell and Hungerford's discovery would soon be called the "Philadelphia Chromosome." For them, it suggested a genetic cause for leukemia. But others weren't so sure. It could also be the other way around, that leukemia caused chromosomal damage.

PETER NOWELL, MD: Some people didn't want to believe that a genetic alteration was involved in the development of cancer. And when I talk about "genetic" here, I'm talking about somatic genetics. This is a change in one cell that allows the progeny of that cell to grow out as a tumor.

JOHN M. GOLDMAN, MD: There was quite a period during which there was a legitimate debate as to whether this Philadelphia chromosome was just a marker, was just an index of something gone wrong or whether it was actually the cause of the real pathogenesis of this disease.

ANNOUNCER: Nowell and Hungerford had discovered that patients with chronic myeloid leukemia-or CML-often had a chromosome that was missing a piece. It took more than a decade before anyone found what happened to it.

JOHN GOLDMAN, MD: Not much happened until 1973 when Janet Rowley, a very eminent cytogeneticist working in Chicago, discovered that in fact, it was not loss of chromosomal material from chromosome 22, it was exchange of chromosomal material between 9 and 22. So 22 became shorter and 9 became longer.

JANET ROWLEY, MD: There were new technical advances that occurred in 1970, leading to chromosome banding where there is a unique pattern of dark and light staining areas on chromosomes.

ANNOUNCER: Janet Rowley and other scientists now could distinguish clearly among the 23 chromosomes pairs in the human cell. And by analyzing photographs of leukemia cells taken under a microscope, Rowley solved the puzzle. She found out what had happened to the missing piece of the Philadelphia chromosome. Two chromosomes switched parts, what's called a "translocation." Rowley made her discovery at home, where she often worked while raising children.

JANET ROWLEY, MD: I worked on the dining room table because it was the biggest, clear surface in the house where you could spread out 15 or 20 photographs and look first at one and then another and then see that the same abnormality was present. It was a moment of great elation because I was not looking for translocations; they didn't exist.

ANNOUNCER: Ten years later, researchers started understanding the genetic damage caused by the translocation. They learned it created a new gene called BCR-Able.

JOHN GOLDMAN, MD: So you now have on the Philadelphia chromosome a fusion gene composed of parts of two normal genes, which never normally come together.

ANNOUNCER: The new gene creates an enzyme that interferes with signals that regulate white blood cells, causing an explosion in their growth, the hallmark of chronic myeloid leukemia.