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Down Syndrome (Trisomy 21)

What is Down syndrome, and what causes it?

Down syndrome is a genetic disorder.  Most people have 46 chromosomes in each cell.  Children with Down syndrome have 47 chromosomes.  They have an extra copy of chromosome 21.  Normally, we inherit 23 chromosomes from our mother and 23 chromosomes from our father (for a total of 46).  Babies with Down syndrome inherit an extra copy of chromosome 21 leading to 3 copies (one from Mom, one from Dad, plus one extra).  We call this Trisomy 21

Some children have mosaic Down syndrome or mosaicism. In this type of Down syndrome, not all cells have the extra chromosome, which can result in the child being less severely affected.

To learn more about genetics and to better understand how genes cause syndromes, see YourChild: Genetic Syndromes.

How common is Down syndrome?

Down syndrome is the most common single cause of human birth defects.   About 1 out of every 660 babies is born with Down syndrome.[1]

How is it diagnosed?

Down syndrome can either be diagnosed in utero (via amniocentesis) or, most commonly, after birth. After birth, it can usually be diagnosed based on distinctive physical features:

The baby’s blood can be tested to confirm the Trisomy 21.

Where do we get started as new or expectant parents of a baby with Down syndrome?

A good starting place is downloading, printing, and reading the brochure A Promising Future Together:  A guide for new and expectant parents from the National Down Syndrome Society.  This brochure addresses many issues including health concerns, growth and development, early intervention, finding support, and family and sibling dynamics. It also includes resource lists at the end of each section. You can also watch the video: A Promising Future Together.

This film came out in 2003, and covers everything new parents need to know in the first 18-24 months—all covered in a positive and empowering way.  Features interviews with experts and parents, and footage of adorable babies.

How will my child grow and develop?

Most children with Down syndrome will learn to walk, speak, think, and solve problems in their own time. Most have some degree of intellectual disability.

They generally grow more slowly, learn more slowly, and have more trouble with reasoning and judgment than other children. They often have a short attention span. They might be impatient, and quick to grow frustrated or angry.

Children with Down syndrome generally should not be compared in their development with other children. Here are resources for growth and developmental milestones unique to children with Down syndrome:

What do I need to think about as my child enters the teen years and adulthood?

As your child matures, you will need to address their transition to adulthood. The following links cover social, legal, financial, and independence issues, sexuality, employment, and transition planning for life after high school:

What are the health concerns for children with Down syndrome?

Children with Down syndrome are more likely to have heart defects, gastrointestinal (gut) blockages, and also have a higher likelihood of leukemia than kids without Down syndrome.

This fact sheet about Down syndrome has a helpful review of the common health problems you need to know about.

What are the treatments and therapies my child might benefit from?

There is no cure for Down syndrome, but there are many treatments that can help your child.

What books and DVDs about Down syndrome might be helpful?

This book is chock-full of information that is helpful to parents of a child with Down syndrome.  It does discuss all the possible medical problems, which can be scary for new parents. 

What are some other sources of information and support?


[1] Down syndrome.  Medline Plus Medical Encyclopedia.  Available at:  Accessed 22 January 2007.

Compiled by Kyla Boyse, R.N. Reviewed by faculty and staff at the University of Michigan.

Updated November 2009

U-M Health System Related Sites:
U-M Pediatrics
C.S. Mott Children's Hospital Back to top