Study sheds light on how Down's prevents cancer

[Guest guest]

y Maggie Fox, Health and Science Editor

WASHINGTON (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 tumours from growing, and this finding may help in the

development of new cancer drugs, the team at s Hopkins University in

Baltimore reported.

Dr. Reeves of s 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 tumour 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.

" It is turning out to be very important because it gives a strong clinical

clue that suggests some humans may be protected against cancer, " Folkman

said.

" Down syndrome is always considered a tragedy for families. But on the

other hand, they bring this huge clinical clue, " Folkman said. The genes

that protect against cancer appear to be separate from the genes known to cause

mental retardation, he added.

" In medical school in 1953 we were taught -- 'oh, by the way, Down

syndrome individuals are protected against cancer'. Everybody asked why and

they said, 'We think it is because they don't live long enough (to develop

it),' " Folkman said.

But now Down's patients live into their 70s and they still develop cancer at

a lower rate, he said.

Dr. Threadgill of the University of North Carolina agreed that Ets2

might be used as the basis of a drug, but said far more research is needed

because the protein also appears to help cancer spread, or metastasize, when it

does develop.

" So therapeutic use of potential drugs with Ets2-like activity to

reduce tumour incidence may have limited value, because a side effect of such

drugs could be increased efficiency of metastasis, " Threadgill wrote in a

commentary. (Editing by Alan Elsner)

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