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Down syndrome

The term "syndrome" is applied to any condition or disease which has several physical and or cognitive (mental) findings that vary from what is generally considered normal and which, when observed together, form a distinctive patter that suggests a specific diagnosis. Although Downs syndrome was first recognized during the nineteenth century, only in 1959 was it determined that the conditions is caused by the presence of an extra chromosome 21 in the cells of an affected individuals body.

In the majority of individuals with Dons syndrome the condition results from the presence of an extra chromosome 21 in each cell of the body. The technical notation for this condition is 47,XX,+21 in affected females and 47,XY,+21 in affected males, and is often referred to as trisomy 21. Studies have determined in approximately 70-80% of cases the extra chromosome 21 originates in the mother's egg and 20-30% in the father's sperm. It is also know that a particular woman's risk of having a child with the trisomic form of downs syndrome increases as she ages (beginning at age35). Age of the mother is perceived only as a factor in the occurrence of the condition. It is not known what causes trisomy 21 or why the risk of having an affected child increases in older women.

Why Is This Important?

Down syndrome is the most frequent genetic condition of childhood associated with mental retardation. Studying rates and trends of Down syndrome in Utah helps assess the burden of disease, plan for and distribute the resources needed to serve affected people and families, and estimate future needs. This information can also help monitor population-based survival and the level of preventive care provided to people with Down syndrome The Utah Birth Defects Network tracks Down syndrome since 1995.

The diagnosis of Down syndrome is confirmed with cytogenetic testing that shows the additional chromosome 21 (or piece of 21) that is diagnostic for this condition.

Children with Down syndrome are frequently born with additional structural malformations that can significantly affect their health and that often require surgical and medical treatment. The most common malformations occurring in children with Down syndrome are congenital heart malformations (50%). The American Academy of Pediatrics (AAP) has developed recommendations for health, supervision, and anticipatory guidance infants and children with Down syndrome, to prevent complications and improve long term health and survival by identifying early associated conditions and risk factors for morbidity. For example, the Academy recommends that all babies with Down syndrome have a pediatric cardiac evaluation with echocardiogram in the first month of life.

Several studies show that now, with better clinical care and social support, people with Down syndrome are living longer. With appropriate care, people with Down syndrome can expect to live long lives, with varying degrees of independence in the community.

The primary known risk factor for Down syndrome is advanced maternal age. Awareness of this association can help understand population rates of Down syndrome, project future number of affected births based on the trends in age-specific birth rates, and provide a basis for primary prevention of this condition.

How Are We Doing?

In 2003, the UBDN reports a rate of Down syndrome in Utah of 1 in 580 births (or 17.1 per 10,000 births). Since 1995, when the UBDN began tracking rates of Down syndrome, such rates have remained stable (Figure 1). Rates are much higher among women 35 years of age or older and this too has been constant over time (Figure 2). Risk of having an affected pregnancy increases considerably and very quickly after age 35 (Figure 3). In Utah, women 35 years of age or older contribute to 9% of all births but experience 42% of all pregnancies with Down syndrome.

To date, there is no evidence to suggest that the prevalence of Down syndrome is increased within any particular racial group.

In absolute numbers, approximately 80 affected pregnancies occur every year in Utah, with a cumulative total of approximately 650 cases from 1995 through 2003 (Figure 4).

How Does Utah Compare With the U.S.?

Because Down syndrome is determined by a chromosomal condition whose risk seems to depend essentially on maternal age only, the occurrence of Down syndrome in different populations seems to reflect the population's maternal age distribution, with little variation due to other factors.

We would expect to see in Utah rates of Down syndrome at least as high or even higher than in other parts of the United States, for several reasons. In Utah the birth rate is high, and pregnancies tend to occur also at the higher end of childbearing age.

Overall rates of Down syndrome in Utah (15.3 per 1,000 births for 1995 through 2003) are similar to those observed in the Atlanta registry in Georgia (15.2 per 1,000 births for 1994-1999). Such comparison is meaningful because the Atlanta registry (MACDP), which is run by the Centers for Disease Control and Prevention, uses tracking methods similar to those in the Utah Birth Defect Network.

Rates among women 35 years of age or older appear to be higher in Utah (72.4 per 1,000 women of that age) than in Atlanta (53.3 per 1,000). This higher rate could depend on the wider age distribution at birth in Utah. Because risk for Down syndrome increases greatly for every year above 35 and particularly above 40, even small differences between Utah and Atlanta with respect to the number of pregnancies occurring in these higher maternal age groups could considerably affect the observed occurrence rates.

What Is Being Done?

The American Academy of Pediatrics has outlined specific recommendations for Down syndrome children. These recommendations cover several time periods from birth to 21 years and older. Details are available on the American Academy of Pediatric web site: http://www.aap.org/

Specific services for families of affected children from birth to three years of age are provided by the Utah Early Intervention Program, located within the Bureau of Children with Special Health Care Needs, Utah Department of Health. Services include child health assessment, service coordination among providers, programs and agencies, occupational and physical therapy, speech and language therapy. Information on these services is available at http://www.utahbabywatch.org

A further resource is the Utah Collaborative Medical Home, which is a project designed to provide information, tools and resources for Primary Care Physicians to enhance their ability to care for children with special health care needs. Information on the Utah Collaborative Medical Home is available at their web site: www.medhomeportal.org

Graphics
• Overall rate per 10,000 by year
. Rate by maternal age (<35 years, 35+) by year
. Rate by 5-year class of maternal age
. Number of affected births per year (since 1995)