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Why should we be concerned about Down syndrome? Chromosomal abnormalities are a widespread medical problem, with Down syndrome being the most common genetic condition. One in every 800 to 1,000 children is born with Down syndrome. More than 50 percent of miscarriages are caused by a chromosomal abnormality. As many as 25 percent of all miscarriages are caused by a trisomy, which is the presence of three copies of a particular chromosome, rather than the normal two. The most common form of Down syndrome is called Trisomy 21, because it involves an extra copy of the 21st chromosome. Twenty to 25 percent of children conceived with Down syndrome survive past birth. What impact does Down syndrome have on society? Individuals with Down syndrome are becoming increasingly integrated into society and community organizations, such as school, health care systems, work forces and social and recreational activities. Individuals with Down syndrome possess varying degrees of mental retardation, from very mild to severe. Most people with Down syndrome have IQs in the mild to moderate range of mental retardation. Due to advances in medical technology, individuals with Down syndrome are living longer than ever before. In 1910, children with Down syndrome were expected to survive to age nine. With the discovery of antibiotics, the average survival age increased to 19 or 20. Now, with recent advancements in clinical treatment, as many as 80 percent of adults with Down syndrome reach age 55, and many live even longer. In the United States, approximately 350,000 families are affected by Down syndrome. Approximately 5,000 children with Down syndrome are born each year. As the mortality rate associated with Down syndrome is decreasing, the prevalence of individuals with Down syndrome in our society will increase. Some experts project that the number of people with Down syndrome will double in the next 10 years. More and more Americans will interact with individuals with this genetic condition, increasing the need for widespread public education and acceptance. Who has the highest risk of having a child with Down syndrome? Down syndrome affects people of all races and economic levels. Women age 35 and older have a significantly increased risk of having a child with Down syndrome. A 35-year-old woman has a one in 400 chance of conceiving a child with Down syndrome and this chance increases gradually to one in 110 by age 40. At age 45 the incidence becomes approximately one in 35. Since many couples are postponing parenting until later in life, the incidence of Down syndrome conceptions is expected to increase. Therefore, genetic counseling for parents is becoming increasingly important. Still, many physicians are not fully informed about advising their patients about the incidence of Down syndrome, advancements in diagnosis and the protocols for care and treatment of babies born with Down syndrome. Why are medical researchers following Down syndrome work so closely? Down syndrome is a developmental disorder. As researchers learn more about the molecular genetics and other aspects of Down syndrome, they also obtain valuable information about human development and can advance the study of many biological processes. In addition, individuals with Down syndrome have a higher incidence of certain medical problems and the study of Down syndrome may yield important breakthroughs in those areas. Research in Down syndrome provides a way for looking at many important problems: Heart disease: Up to 50 percent of individuals with Down syndrome are born with congenital heart defects. The majority of heart defects in children with Down syndrome can now be surgically corrected with resulting long-term health improvements. However, scientists continue to search for the cause of this problem and look for means of prevention. Alzheimer's disease: Estimates vary, but it is reasonable to conclude that 25 percent or more of individuals with Down syndrome over the age of 35 will develop the clinical signs and symptoms of Alzheimer's-type dementia. Leukemia: Individuals with Down syndrome have a 15 to 20 times greater risk of developing leukemia. The majority of cases are categorized as acute megakaryoblastic leukemia, which tends to occur in the first three years of life, and for which there is a high cure rate. A transient form of leukemia is also seen in newborns with Down syndrome, disappearing spontaneously during the first two to three months of life.
Down syndrome Try telling this to someone: “Children with Down syndrome are at a much higher risk for leukemia.” Then watch the person hearing this for the first time. You’ll see shock and compassion. They will say, “That just isn’t fair!” But, sadly, it happens. It has been known for some time that the incidence of leukemia in children with Down syndrome is greatly increased in comparison with the general population. It is estimated that the risk of leukemia for children under 10 years of age is increased by at least 18 times if they have Down syndrome. One in every 95 children with Down syndrome develops leukemia, compared with one in every 2000 children without Down syndrome. This still means that the vast majority of children with Down syndrome will never develop leukemia, but it is a risk that offers considerable challenges. The explanation for the increased risk? Most patients with Down syndrome have been found to have three instead of two copies of chromosome 21 in every cell of their body. This results in the malformation and dysfunction of various organs and systems, including the respiratory system, the cardiovascular system, the central nervous system, the endocrine glands, and the immune system. It appears that the extra genetic material found on chromosome 21 also may cause stem cells to proliferate before they have developed to maturity, creating “blast cells,” and thus, leukemia. Further complicating the situation when a child with Down syndrome is battling a blood disease is the fact that they have a far greater risk of mortality due to infection than other children – primarily respiratory infections. Two forms of leukemia, two different stories Children with Down syndrome are usually diagnosed with one of the two major forms of leukemia -- ALL (acute lymphoblastic leukemia) and AML (acute myeloid leukemia) -- in about the same proportion as all other children. One bit of good news: compared to most children with AML, children who also have Down syndrome respond to treatment better, and have survival rates as high as 85%, compared with 50-55% for the others. The ALL story is somewhat different. Twenty years ago, it seemed that survival statistics for children with Down syndrome lagged behind the other ALL patients. However, according to Nyla Heerema, PhD, chair of the Cytogenetics Committee of the Children’s Oncology Group (COG): “In a recent analysis of 1880 children with ALL who were treated on protocols between 1988 and 1995, there were 34 children with Down syndrome. Outcome was not statistically different for DS (Down syndrome) and non-DS patients.” However, Dr. Heerema points out, the incidence of deaths related to toxicity was greater for DS than for non-DS patients. Clearly, more research must be done to study the various chemotherapy agents and how the child with DS metabolizes those chemicals differently. Environmental triggers sought Julie Ross, PhD, a childhood cancer epidemiologist at the University of Minnesota, is conducting a national study, with CCG investigators, looking at the environmental and biological factors that may influence the development of leukemia in children with Down syndrome. Parents of Down syndrome and non-Down syndrome children with leukemia are being asked to complete extensive questionnaires about their employment, lifestyle, and medical history. Some factors have already been modestly associated with an increased risk of childhood leukemia, so it will be especially informative to compare these factors in children with Down syndrome who already are at a higher risk of developing leukemia. Children with Down syndrome and their parents face major life challenges. When the child also develops leukemia, the demands upon that family are multiplied. Perhaps the most positive element in the situation is that children with Down syndrome may eventually provide a better understanding of the genetics of leukemia in all children. |