While people with Down syndrome have a high chance of developing childhood leukemia, a new study shows they have only half the normal lifetime risk of getting other kinds of cancer. Experts already knew about the leukemia risk faced by people with Down syndrome, but the study by Danish scientists is the first to estimate their chances of developing other cancers.
The study, published in this week's issue of The Lancet Medical Journal, suggests those with Down syndrome may be protected because they have an extra copy of a chromosome that contains cancer-fighting genes. Normally, people have two copies of each chromosome - one from each parent - but those with Down syndrome have three copies of chromosome 21, which has at least one gene linked to leukemia.
Scientists suspect the 10-fold increased risk of leukemia among those with Down syndrome could be related to having the extra copy of the gene. The researchers could not say why people with Down syndrome appeared to be less vulnerable to other cancers, but scientists have identified several genes on chromosome 21 that they suspect could help curtail the growth of cancerous tumors. The findings provide a clue that there might be more protective genes on chromosome 21 to identify.
"Further studies on these putative genes may have implications for the understanding of (how cancer develops) and eventually the prevention of cancer in the general population," said the study's leader, Dr. Henrik Hasle, a childhood cancer specialist at Skejby Hospital at Aarhus University in Denmark.
In the study, the occurrence of cancer in 2,814 people with Down syndrome was compared to that in the general Danish population. The research looked at cancer occurring at any time from birth to old age. Those with Down syndrome tend to die early, partly because they have heart defects and develop Alzheimer's disease much sooner than normal. Many die before they reach the age when tumors commonly develop.
But the study found that even after adjusting for their shorter life expectancy, those with the syndrome had a 50 percent lower risk of non-leukemia cancers, compared with their counterparts of the same age. The advantage remained consistent regardless of their age. "The finding that the decreased risk persisted in the older age groups is of considerable importance for the future," said Charles Stiller, an epidemiologist at the childhood cancer research group at England's Oxford University, which was not connected to the study.
"Long-term survival in Down syndrome people is more common these days, and this study suggests that Down syndrome people with a normal lifespan will be less vulnerable to cancer than other people," Stiller said. "Once one is past the period of raised risk of leukemia in childhood, the overall cancer risk is appreciably lower than in the general population." The most significant advantage was seen in breast cancer, according to the study. The scientists expected to see seven cases among the Down syndrome group, based on what occurs normally, but they found none. They found no new cases of leukemia after the age of 29. The researchers acknowledged that the drop in risk for some of the cancers could be due in part to non-genetic reasons such as a healthier lifestyle.
Reprinted with Permission by Associated Press
This article first appeared in issue #9 of Down Syndrome Amongst Us