Down syndrome is a condition in which a person has an extra chromosome. Chromosomes are small “packages” of genes in the body. They determine how a baby’s body forms during pregnancy and how the baby’s body functions as it grows in the womb and after birth. Typically, a baby is born with 46 chromosomes. Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. A medical term for having an extra copy of a chromosome is ‘trisomy.’ Down syndrome is also referred to as Trisomy 21. This extra copy changes how the baby’s body and brain develop, which can cause both mental and physical challenges for the baby.
a congenital disorder arising from a chromosome defect, causing intellectual impairment and physical abnormalities including short stature and a broad facial profile. It arises from a defect involving chromosome 21, usually an extra copy (trisomy-21).
Down Syndrome DEFECT
Down syndrome is a condition in which extra genetic material causes delays in the way a child develops, both physically and mentally.
Down syndrome continues to be the most common chromosomal disorder. Each year, about 6,000 babies are born with Down syndrome, which is about 1 in every 700 babies born.1
Between 1979 and 2003, the number of babies born with Down syndrome increased by about 30%.
Older mothers are more likely to have a baby affected by Down syndrome than younger mothers. In other words, the prevalence of Down syndrome increases as the mother’s age increases. Prevalence is an estimate of how often a condition occurs among a certain group of people. To estimate the prevalence of Down syndrome, the number of pregnancies affected by Down syndrome is compared to the total number of live births.
Many people with Down syndrome have the common facial features and no other major birth defects. However, some people with Down syndrome might have one or more major birth defects or other medical problems. Some of the more common health problems among children with Down syndrome are listed below.8
Hearing loss (up to 75% of people with Down syndrome may be affected)
Obstructive sleep apnea, which is a condition where the person’s breathing temporarily stops while asleep (between 50 -75%)
Ear infections (between 50 -70%)
Eye diseases (up to 60%), like cataracts and eye issues requiring glasses
Heart defects present at birth (50%)
Other less common health problems among people with Down syndrome include:
Intestinal blockage at birth requiring surgery
Anemia (red blood cells can’t carry enough oxygen to the body) and iron deficiency (anemia where the red blood cells don’t have enough iron)
Leukemia in infancy or early childhood
Health care providers routinely monitor children with Down syndrome for these conditions. If they are diagnosed, treatment is offered.
Types of Down Syndrome
There are three types of Down syndrome. People often can’t tell the difference between each type without looking at the chromosomes because the physical features and behaviors are similar.
Trisomy 21: About 95% of people with Down syndrome have Trisomy 21.2 With this type of Down syndrome, each cell in the body has 3 separate copies of chromosome 21 instead of the usual 2 copies.
Translocation Down syndrome: This type accounts for a small percentage of people with Down syndrome (about 3%).2 This occurs when an extra part or a whole extra chromosome 21 is present, but it is attached or “trans-located” to a different chromosome rather than being a separate chromosome 21.
Mosaic Down syndrome: This type affects about 2% of the people with Down syndrome.2 Mosaic means mixture or combination. For children with mosaic Down syndrome, some of their cells have 3 copies of chromosome 21, but other cells have the typical two copies of chromosome 21. Children with mosaic Down syndrome may have the same features as other children with Down syndrome. However, they may have fewer features of the condition due to the presence of some (or many) cells with a typical number of chromosomes.
Down syndrome is a lifelong condition. Services early in life will often help babies and children with Down syndrome to improve their physical and intellectual abilities. Most of these services focus on helping children with Down syndrome develop to their full potential. These services include speech, occupational, and physical therapy, and they are typically offered through early intervention programs in each state. Children with Down syndrome may also need extra help or attention in school, although many children are included in regular classes.
Eat properly and take prenatal vitamins before and during pregnancy. Also take folic acid supplements as instructed by your doctor. Reduce your risks for infections during pregnancy. Some infections can increase the risk that a fetus will develop cleft lip or cleft palate.
1. Parker SE, Mai CT, Canfield MA, et al. Updated national birth prevalence estimates for selected birth defects in the United States, 2004-2006. Birth Defects Res A Clin Mol Teratol. 2010;88:1008-16.
2. Shin M, Siffel C, Correa A. Survival of children with mosaic Down syndrome. Am J Med Genet A. 2010;152A:800-1.
3. Allen EG, Freeman SB, Druschel C, et al. Maternal age and risk for trisomy 21 assessed by the origin of chromosome nondisjunction: a report from the Atlanta and National Down Syndrome Projects. Hum Genet. 2009 Feb;125(1):41-52.
4. Ghosh S, Feingold E, Dey SK. Etiology of Down syndrome: Evidence for consistent association among altered meiotic recombination, nondisjunction, and maternal age across populations. Am J Med Genet A. 2009 Jul;149A(7):1415-20.
5. Sherman SL, Allen EG, Bean LH, Freeman SB. Epidemiology of Down syndrome. Ment Retard Dev Disabil Res Rev. 2007;13(3):221-7.
6. Adams MM, Erickson JD, Layde PM, Oakley GP. Down's syndrome. Recent trends in the United States. JAMA. 1981 Aug 14;246(7):758-60.
7. Olsen CL, Cross PK, Gensburg LJ, Hughes JP. The effects of prenatal diagnosis, population ageing, and changing fertility rates on the live birth prevalence of Down syndrome in New York State, 1983-1992. Prenat Diagn. 1996 Nov;16(11):991-1002.
8. Bull MJ, the Committee on Genetics. Health supervision for children with Down syndrome. Pediatrics. 2011;128:393-406.
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