By Maggie Fox, Health and Science Editor Maggie Fox, Health And
> Science Editor -- Wed May 20, 1:45 pm ET
>
> WASHINGTON (Reuters) -- People with Down's syndrome rarely get most
> kinds of cancer and U.S. researchers have nailed down one reason why
> -- they have extra copies of a gene that helps keep tumors from
> feeding themselves.
>
> The findings could lead to new treatments for cancer, the researchers
> reported in the journal Nature on Wednesday, and further study of
> Down's patients might reveal more ways to fight tumors.
>
> The researchers at Harvard University and elsewhere made use of a new
> kind of embryonic-like stem cell called an induced pluripotent stem
> cell or iPS cell. These cells, made from ordinary skin, can be
> transformed to act like powerful stem cells, the body's master cells.
>
> Using iPS cells from a volunteer with Down's syndrome and mice
> genetically engineered to have a version of the condition, the
> researchers pinpointed one gene that protects against tumors.
>
> "It is, perhaps, inspiring that the Down's syndrome population
> provides us with new insight into mechanisms that regulate cancer
> growth," they wrote.
>
> Down's syndrome is the most common genetic cause of mental
> retardation, occurring in 1 out of 700 live births.
>
> The Down's syndrome theory had long been explored by Harvard's Dr.
> Judah Folkman, who died last year. Folkman, whose name is on the
> study, developed theories about how tumor cells grow blood vessels to
> nourish themselves in a process called angiogenesis.
>
> EXTRA GENES
>
> Folkman also noticed how rare cancer is among Down's patients, except
> for leukemia, and he wondered whether the genes explain why. A study
> of nearly 18,000 Down's patients showed they had 10 percent the
> expected rate of cancer.
>
> People with Down's syndrome have a third copy of chromosome 21, where
> most people have two copies. The extra copy gives them extra versions
> of 231 different genes.
>
> "One such gene is Down's syndrome candidate region-1 (DSCR1, also
> known as RCAN1)," Harvard's Sandra Ryeom and colleagues wrote.
>
> This gene codes for a protein that suppresses vascular endothelial
> growth factor or VEGF -- one of the compounds necessary for angiogenesis.
>
> Down's patients have extra amounts of this DSCR1 protein, as do the
> genetically engineered Down's mice, the researchers showed.
> Genetically engineered mice with an extra copy of DSCR1 were resistant
> to tumors.
>
> DSCR1 affects a compound called calcineurin, long a focus of cancer
> research.
>
> "These data provide a mechanism for the reduced cancer incidence in
> Down's syndrome," the researchers wrote.
>
> The study also provides three new potential targets for preventing or
> treating cancer -- calcineurin and two genes that regulate it, DSCR1
> and DYRK1A, they said.
>
> People with Down's syndrome are also less likely to develop
> angiogenesis-related diseases such as diabetic retinopathy (an eye
> disease related to diabetes) and atherosclerosis (hardened arteries),
> "suggesting that cancer protection ... may be due, in part, to
> angiogenesis suppression," the researchers wrote.
>
> "Because human chromosome 21 contains over 200 genes, it would be
> surprising if DSCR1 was the only chromosome 21 gene implicated in
> tumor suppression in Down's syndrome individuals," they said.
>
> (Editing by John O'Callaghan)
>
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