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Chromosomal Abnormalities: Trisomy 21

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Down syndrome and chromosomal abnormality trisomy 21 iStockphoto/Thinkstock

Trisomy 21, the most common type of Down syndrome, is a chromosomal abnormality where the developing embryo receives three chromosome 21s instead of the usual two.

Normally, a baby inherits one copy of chromosome 21 from his mother’s egg and one copy from his father’s sperm.

In Trisomy 21, one of the gametes (egg or sperm) has two copies so the baby ends up with too much genetic information. This extra genetic information results in varying degrees of physical and intellectual disability.

Trisomy 21 affects 94 percent of those with Down syndrome. There are two other types, translocated Down syndrome, where the extra chromosome 21 is attached to another chromosome (this accounts for 4 percent of cases) and mosaic Down syndrome, where only some cells in the body have the extra chromosome 21. This is the rarest kind, affecting only 2 percent.

Down syndrome was named after a British doctor called John Langdon Down, who described the syndrome in 1866. However, it had already been described by another doctor, Jean Etienne Dominique Esquirol in 1838.

Signs of Down Syndrome

Signs of Down Syndrome include:

• Characteristic facial features like a flat nose, upward slanting eyes, white spots on the iris and abnormally shaped ears

• A small mouth that makes the tongue look too big – sometimes the tongue will protrude

• Smaller than average fingers with a little finger that curves inwards

• Smaller than average feet and a big space between the big toe and the second toe on each foot

• Deep creases in the palms of the hands

• Poor muscle tone and loose ligaments resulting in floppiness

• Lower than average birth size and weight

Children with Down syndrome often have other co-existing medical conditions such as congenital heart disease, hearing problems, eyesight problems, celiac disease, skeletal abnormalities, thyroid dysfunction and dementia.

Some children have gastrointestinal and immune system problems. Around 10 percent of children with Down syndrome also have autism.

Some babies have difficulty with feeding because their mouth and tongue shape are different from normal. As their muscle tone is weak, their suck reflex will also be weak. Babies with Down syndrome tend to be more placid and sleepy and prone to falling asleep at the breast, so occasionally new moms will find it hard to breastfeed.

However, it is really important to try and breastfeed a baby with Down syndrome because breast milk will provide immunity from infections and help prevent or ease any intestinal problems the baby has.

Breastfeeding can also improve the baby’s mouth and tongue coordination which gives him an advantage against others who are formula fed.

La Leche League International can provide advice and support to mothers who wish to breastfeed their baby with Down syndrome.

See: http://www.llli.org/faq/down.html/

Some babies, however, don’t have any trouble breastfeeding at all and have no additional health problems, so it really depends on the individual baby.


Babies and toddlers are often delayed in their milestones (for instance, they usually learn how to talk later than typical children).

They will require early intervention and special educational services but they can usually be educated in mainstream schools and further education colleges. Many are able to work and have relationships, although social services support or sheltered housing may be required.

Some have even gone into high profile careers like acting. For instance, Stephane Ginnsz was the first actor with Down syndrome to play the lead role in a film.


Down’s Syndrome: Children Growing Up. Janet Carr, Oxford University Press, 24th November 1995.
Down Syndrome Through the Ages, Med Gadget. Web. 25 April 2012. http://medgadget.com/2005/11/down_syndrome_t.html

Down Syndrome, Eunice Kennedy Shriver National Institute of Child Health and Human Development. Web. 25 April 2012. http://www.nichd.nih.gov/health/topics/Down_Syndrome.cfm#TheOccurrence

Information for Parents: Down Syndrome, leaflet. Web. 25 April 2012. http://www.downs-syndrome.org.uk/images/stories/DSA-documents/Publications/education/information_for_parents_down_syndrome_2010_ed.pdf

Is it possible to breastfeed my baby who was born with Down Syndrome? La Leche League International. Web. 25 April 2012. http://www.llli.org/faq/down.html

Stephane Ginnsz Official Website. Web. 25 April 2012. http://www.stephane.ginnsz.com

Joanna is a freelance health writer for The Mother magazine and Suite 101 with a column on infertility, http://infertility.suite101.com/ She is the mother of five children and practices natural childbirth, delayed cord clamping, full term breastfeeding and organic food diet.

Reviewed April 25, 2012
by Michele Blacksberg RN
Edited by Jody Smith

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