THURSDAY, March 21, 2002 (HealthDayNews) -- People with Down syndrome are living longer than ever before -- almost twice as long.
New research chalks up the improvement to improved medical care and the trend away from institutional living for those with Down syndrome, a form of mental retardation. But not all of the news is good. The study found racial disparities in death rates and high rates of leukemia among those with the condition.
The findings appear in the March 23 issue of The Lancet.
Down syndrome is the result of a chromosomal abnormality, in which people with the disorder have 47 rather than 46 chromosomes in each cell from an extra partial or complete copy of one pair of chromosomes.
More than 350,000 Americans have Down syndrome. It's associated with varying degrees of mental retardation, and children with Down syndrome may take longer to reach certain basic developmental milestones. Among the most common traits associated with the disorder are low muscle tone, a flattened facial profile, an upward slant to the eyes, small skin folds on the eyes' inner corners, and abnormal ear shape.
In the latest study, researchers at the Centers for Disease Control and Prevention in Atlanta and the University of British Columbia in Vancouver, B.C., used U.S. death certificates from 1983 to 1997 to identify 17,897 people reported to have Down syndrome.
Study co-investigator Dr. Sonja Rasmussen, a clinical geneticist at the CDC's National Center on Birth Defects and Developmental Disabilities, calculated age of death and death rates from common medical conditions.
Her team found that over the span of time analyzed, the average age of death among people with Down syndrome almost doubled, from 25 to 49 years of age. However, Rasmussen and her team also found "significant racial disparities" between white people with Down syndrome and black people or people of other races with the condition, although the study notes that the gap began to close in 1992.
The team also noted dramatic differences in cancer rates among people with Down syndrome. Compared to records of the general population, the researchers found records of malignancy were less than 10 percent as likely among people with Down syndrome. While the rates of leukemia and testicular cancer were higher among those with the condition, tumors including breast, lung and colon cancer were significantly less common.
Dr. Charles Epstein, a professor of pediatrics and the chief of medical genetics at the University of California, San Francisco, says the data on the low incidence of cancers is intriguing. "The numbers are impressively low," he says. "It suggests that there's something really worth looking at on chromosome 21 [a prevalent predictor of Down syndrome] that's having quite a profound effect on tumor suppression."
Rasmussen says it's not yet known why most cancers are less common in persons with Down syndrome, but there are several theories. "We know that several cancers are related to environmental exposures like smoking or alcohol or certain occupational exposures, and it's likely that people with Down syndrome have reduced exposure to those factors," she says.
A second theory suggests that since cells replicate more slowly in people with Down syndrome, the errors that normally crop up during cell reproduction occur less frequently.
A third theory suggests that there are critical tumor genes on chromosome 21. Since those with Down syndrome have an extra copy of the chromosome, they may have three, rather than two, copies of those genes. Since the odds of abnormalities in all three copies of the genes are lower than in two copies, it may provide the equivalent of a backup set of brakes on tumor growth.
Rasmussen says the findings open the door for future studies to explore why the incidence of many cancers is less among people with Down syndrome. "That might provide us with some insight into what genes cause cancer," she says.
She says that medical care has improved dramatically, both in terms of methods for treating congenital heart defects common in children born with Down syndrome and in ensuring that Down syndrome patients are offered necessary surgical procedures, which hasn't always been the case.
"The way that society treats persons with Down syndrome has changed a lot in the last few decades," says Rasmussen. "Previously, babies with Down syndrome were often institutionalized, and today most children with Down syndrome live with their families; older persons with Down syndrome live in either group homes or in the community."
Her team is currently looking into the details of differences in longevity between people of different races with Down syndrome revealed by this study. "We really need to eliminate these racial disparities," she says. The study didn't specify how great the racial differences were. Epstein only says that the racial disproportion seen in this study "parallels the disparities which we see in all types of health care." A graph that was part of the study indicated that between 1983 and 1992, blacks with Down syndrome lived less than half as long as whites with the condition.
He adds that since people with Down syndrome are living longer, researchers and clinicians need to find ways to further improve their medical care to provide health and quality of life along with longevity. "It's no longer a condition in which one looks forward to a markedly shortened life expectancy that's filled with a lot of illnesses," says Epstein.
What to Do: Find out more about Down syndrome from the National Down Syndrome Society, the National Institute of Child Health and Human Development or the March of Dimes.
