Study sheds light on how Down's prevents cancer

By Maggie Fox, Health and Science Editor

WASHINGTON, Jan 2 (Reuters) - People with Down's syndrome suffer cancer less than most other people and a study in mice published on Wednesday gives one possible explanation -- they produce higher levels of a certain protein.

The protein may keep tumors from growing, and this finding may help in the development of new cancer drugs, the team at Johns Hopkins University in Baltimore reported.

Dr. Roger Reeves of Johns Hopkins and colleagues found a gene called Ets2 protected mice from colon cancer. Writing in the journal Nature, Reeves and colleagues said they used mice bred to develop colon cancer at extreme rates, and genetically engineered them to produce extra amounts of Ets2.

They said the more Ets2 the mice had, the less likely they were to develop colon cancer.

The secret lies in having an extra copy of chromosome 21. People with Down's syndrome, also known as Down syndrome, have three copies of the chromosome instead of the usual two.

That gives them extra copies of all the genes on chromosome 21 and of the proteins that these genes produce.

The effects are well known -- people with Down's suffer from mental retardation, have distinct facial and other physical characteristics and a higher risk of some diseases.

But not cancer, said Dr. Judah Folkman, a cancer expert at Children's Hospital and Harvard Medical School in Boston. Ets2, which is found on chromosome 21, may help explain why.

"They are protected against cancer and also atherosclerosis and diabetic retinopathy," Folkman, who was not associated with the research, said in a telephone interview.

Diabetic retinopathy can cause blindness in people with diabetes and, like atherosclerosis, is associated with blood vessel function.

STARVING TUMORS

Folkman discovered a protein called endostatin that kick-started a field of cancer drugs called angiogenesis inhibitors. They starve a tumor by stopping it from creating blood vessels to nourish itself.

The basic biological mechanism, which affects blood vessel function and growth, may also underlie other so-called vascular diseases such as atherosclerosis, Folkman said.

Folkman and other researchers believe people with Down's produce extra endostatin naturally, but also that other genes play an important role. Ets2 appears to be one of them.