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Chromosomal Anomalies                             Return to Listing of Selected Birth Defects

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Trisomy 21- Down syndrome

Humans usually have 23 pairs of chromosomes, structures made of DNA that contain the individual's genetic information. Down syndrome is a common genetic birth defect caused by the presence of an extra chromosome 21. The presence of this extra chromosome is associated with a combination of clinical problems, including moderate to severe intellectual disability. Down syndrome also increases the risk for congenital heart defects, gastrointestinal malformations, and childhood leukemia.

The prevalence of Down syndrome at birth in the United States is approximately 13 per 10,000 births. The prevalence of Down syndrome in Florida in 2009 was 12.9 per 10,000 live births.

As is the case with many birth defects, we do not know all of the risk factors that may cause Down syndrome. Maternal age is the most studied risk factor for Down syndrome, and research has shown that the most dramatic increase in Down syndrome risk occurs after age 35. This can be appreciated in the table showing the prevalence of Down syndrome by maternal age in Florida. Studies show that the rate of Down syndrome is similar across ethnic groups. Early intervention programs may help reduce some of the medical, emotional, and social costs associated with this condition.

Intervention strategies for individuals with Down syndrome should be approached from a developmental perspective. Children with Down syndrome often do not demonstrate an even pattern of cognitive development. Strengths are frequently noted in adaptive and social intelligence, while speech and language skills may be comparatively delayed. This unevenness in development demonstrates the need for early and individual assessment of the child's strengths and weaknesses with emphasis on utilizing strengths and compensating for weaker skills. Early intervention includes such services as screening infants for medical problems, providing nutritional meals to young children in low-income settings and helping babies to develop important developmental skills. Early intervention benefits affected children, families and society. Children who receive early intervention show significant improvement in development and learning. Early intervention helps improve the family's self-esteem and enables the family to be their child's best advocate. Appropriate early intervention may reduce the need for more costly special education programs when the child enters school

Trisomy 13-Patau Syndrome and Trisomy 18-Edward's Syndrome

Whereas babies born with Down syndrome have an extra copy of chromosome 21, other babies may have extra copies of other chromosomes. Babies born with an extra copy of chromosome 13 (trisomy 13, Patau syndrome) or chromosome 18 (trisomy 18, Edwards syndrome) usually have severe developmental problems and major malformations. They occur with a combined frequency of about 1 in 4-6,000 births. The extra number 18 or number 13 chromosome usually arises during development of the mother's egg and the problem is not usually inherited. Sometimes a parent may carry an unusual chromosome problem that predisposes to having a child with one of these chromosome abnormalities.

Although the majority of children with these two disorders do not survive beyond two years of age, a significant number do survive into older childhood and young adult years. Trisomy 13 usually is associated with brain malformations and clefts of the lip and palate, as well as internal malformations. Major malformations are less frequent in trisomy 18 but problems of delayed growth and severe neurological abnormalities predominate.

Down Syndrome in Florida - Fact Sheets

down syndrome fact sheet in english        down syndrome fact sheet spanish

*Birth defects image credit: Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities

Information presented does not constitute medical diagnosis or health care advice. Please see a healthcare professional for individual information.