Two Payoffs in the Hunt for Genes

By Joe Levine

Certain types of cancer seem to run in some families, and in the early 1970s a geneticist named Alfred Knudson came up with one explanation: genes that normally protect against the cancer somehow get lost or damaged. Other scientists suggested that these genes serve as "off" switches, restraining cells from replicating ceaselessly and forming malignancies. If the switches are not inherited or are somehow disabled by, say, radiation, chemicals or viruses, cancerous growth might start. Logical enough; but as years passed without hard evidence, people questioned whether such genes existed.

Last week brought vindication for Knudson, now at Philadelphia's Fox Chase Cancer Center. A group of Boston-area scientists announced that they had discovered a gene that normally blocks retinoblastoma, a rare and often hereditary eye cancer that develops in children. The find should lead to an accurate test for genetic susceptibility to the disease and perhaps improved treatment. It has also raised hopes that other genes will soon be found that inhibit the more common cancers of the lung, breast and colon.

Says Team Member Robert Weinberg, an M.I.T. and Whitehead Institute biologist who has done pioneering work in cancer genetics: "Once you understand the origins of a disease, you can work toward its prevention or cure."

On the same day that the retinoblastoma team made headlines, the Muscular Dystrophy Association announced another important find. A group of scientists, led by Louis Kunkel of Boston Children's Hospital, had discovered the gene that, when defective, causes Duchenne muscular dystrophy. The discovery may lead to an effective treatment, even a cure, for the crippling and usually fatal disorder that afflicts 200,000 people in the U.S., most of them young boys.

Both the retinoblastoma and Duchenne genes were located by comparing DNA strands from healthy and diseased cells. The retinoblastoma team, led by Ophthalmologist Thaddeus Dryja of the Massachusetts Eye and Ear Infirmary, found that there are actually two genes in healthy people that protect against the eye cancer -- probably by ordering production of a protein that prevents cells from multiplying uncontrollably. People born with both of these genes intact can usually sustain damage to one without developing retinoblastoma. But those born with one damaged gene nearly always lose the other and develop the disease.

Discovery of the genes, Dryja predicts, will within a year's time result in accurate prenatal and childhood diagnostic tests for retinoblastoma. The next step, he says, will be to find and synthesize the protein ordered by the genes, the one that prevents wild cell proliferation. This still unknown protein might one day be administered to those lacking the gene and could act to halt the disease. Eventually, advances in gene therapy might even lead to a cure, perhaps through the use of bioengineered viruses that would ferry copies of the healthy gene to the cells of a retinoblastoma victim.

Advances in treatment of Duchenne muscular dystrophy could come even faster, particularly synthesis of the protein ordered by a healthy Duchenne gene. According to David Nathan, physician-in-chief at Boston Children's Hospital, "There is a good chance" that work could be accomplished soon enough to benefit today's patients.

With reporting by Christine Gorman/New York and Suzanne Wymelenberg/Boston