Down Syndrome: A Medical Riddle That's Slowly Being Solved
By Dennis Thompson
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FRIDAY, Oct. 22 (HealthDayNews) -- Recent advances have brought welcome gains for the one in every 800 to 1,000 American babies born each year with Down syndrome, the chromosomal abnormality that combines a number of mental and physical birth defects.
People born with the disorder suffer some degree of mental retardation. They also have an increased risk of congenital heart defects, respiratory and hearing problems, childhood leukemia and thyroid conditions.
But those with Down syndrome are living longer than ever, with a life expectancy well into the 50s, and medical advances continue to help ease the symptoms of their birth defect.
October is National Down Syndrome Awareness Month, and doctors are taking the opportunity to share their latest insights into the disorder.
Mia Peterson is a board member of the National Down Syndrome Society. She also has the disorder. She said her struggle goes beyond just her birth defect.
"We want people to become aware of who we are as a person, not as a disability," she said. "We try to get others to become aware of who we are and what we can do, and look at what we can do and not what we can't do."
More than 350,000 people in the United States now live with Down syndrome, and those numbers are expected to rise in the future as more parents have children later in life.
Women aged 35 and older are at significantly higher risk of having a child with Down syndrome, according to the National Down Syndrome Society.
A 35-year-old woman has a one in 400 chance of conceiving a child with Down syndrome, and this chance increases to one in 110 by age 40. At age 45, the incidence becomes approximately one in 35.
There are no measures to keep the birth defect from taking place, said Dr. Bill Cohen, chairman of the National Down Syndrome Society's Clinical Advisory Board.
"Parents can't prevent DS from occurring, since the chromosomal changes occur in the formation of the egg or sperm," Cohen said.
Because of the demographic shift toward older parents, genetic counseling is becoming increasingly important, according to the society. Prenatal testing using amniocentesis or a newer test called chorionic villus sampling can diagnose or, far more likely, rule out Down syndrome, according to the March of Dimes.
Down syndrome occurs when a baby is born with three, rather than two, copies of the 21st chromosome. The additional genetic material alters the course of development, causing the disorder.
Researchers have long focused on a region of chromosome 21, convinced it held the key to many unanswered questions about the disorder.
But results of a mouse-based study published Oct. 22 in Science by Johns Hopkins scientists suggest the genetics of Down syndrome may be far more complicated than thought, diminishing hopes for any near-term breakthroughs.
David L. Nelson, a professor of molecular and human genetics at Baylor College of Medicine who co-wrote an accompanying editorial in the journal, called the study findings "mixed news" for researchers working on Down syndrome.
"The downside is that it makes it less likely that one or a few genes are mostly responsible for Down syndrome, which has been a cherished hope," Nelson said. "The upside is that it gives us a clearer view of how complicated the problem really is."
Doctors generally diagnose Down syndrome at birth based on the baby's appearance. Abnormalities associated with the disorder include:
- Low muscle tone
- A flat facial profile, including a somewhat depressed nasal bridge and a small nose
- An upward slant to the eyes,
- Small skin folds on the inner corner of the eyes
- An abnormal shape of the ears
- Enlargement of the tongue in relationship to the size of the mouth
- A single deep crease across the center of the palm
- Hyperflexibility, or an excessive ability to extend the joints
- Excessive space between large and second toe
Despite the increased health risks for people with Down syndrome, their life expectancy has increased dramatically in recent decades. It has risen from 25 years in 1983 to 56 today.
Research into Down syndrome has focused partly on ways to head off future medical problems for babies that have the disorder, Cohen said.
In particular, scientists are investigating ways to use gene targeting as a means for predicting future problems. Armed with maps of the 21st chromosome, the researchers are honing in on specific genes in the chromosome that cause specific problems.
"The medical community has developed specific recommendations for the early identification of congenital abnormalities in babies with Down syndrome, and also screening protocols to detect conditions which occur more frequently," Cohen said.
Other research has focused on the cognitive effects of Down syndrome. Virtually all adults with Down syndrome over the age of 40 exhibit changes in brain chemistry similar to those of Alzheimer's patients, and scientists hope that research into this similarity could benefit both groups of patients.
Scientists also are investigating drugs that could help ease some of the cognitive effects of Down syndrome. Currently the only proven method of treatment involves a combination of speech, physical, occupational and other therapies.
But medical advances only cover part of the reason why people with Down syndrome are living longer. Cohen said it also has to do with improved integration of the people into the rest of society -- raising children with Down syndrome at home, sending them to the same schools as other kids, and providing them with more meaningful social contact with others.
To learn more, visit the National Down Syndrome Society.
(SOURCES: Bill Cohen, M.D., chairman of the National Down Syndrome Society's Clinical Advisory Board; Mia Peterson, board member, National Down Syndrome Society)
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