Know the Facts

With continued support, we can further the choices and opportunities for those with Down syndrome. The best place to start is to have a basic understanding of what Down syndrome is, who is affected, and the challenges these individuals face.

What is Down syndrome?

Down syndrome is a genetic condition that results when a person is born with three rather than the usual two copies of chromosome 21. Because there are three copies of chromosome 21, Down syndrome is also called “Trisomy 21.”

Are there different types of Down syndrome?

Yes, there are three types:

Trisomy 21, occurs in 95% of cases when there are three, rather than two, number 21 chromosomes present in every cell of the body. Instead of the usual 46 chromosomes, a person with Trisomy 21 has 47. 

Translocation accounts for 4% of all cases. In translocation, part of chromosome 21 breaks off during cell division and attaches to another chromosome, typically chromosome 14. While the total number of chromosomes in the cells remain 46, the presence of an extra part of chromosome 21 causes the characteristics of Down syndrome.

Mosaicism is rare and accounts for 1% of all cases. In mosaicism, nondisjunction of chromosome 21 takes place in one – but not all – of the initial cell divisions after fertilization. When this occurs, there is a mixture of two types of cells, some containing the usual 46 chromosomes and others containing 47. 

What is the frequency of Down syndrome?

Down syndrome is the most frequently occurring chromosomal abnormality, occurring once in every 792 live births.

Does Down syndrome occur in specific people?

Down syndrome occurs equally in people of all ethnic, racial, religious and socio-economic groups.

Is age a factor in Down syndrome?

The rate of births of children with Down syndrome increases with the age of the mother. While the age of the mother can be a factor, 80% of children with Down syndrome are born to parents under the age of 35.

How many people have Down syndrome?

It is estimated that 250,000 people nationwide have Down syndrome. About 4 million people throughout the world have Down syndrome.

Are people with Down syndrome at increased risk for certain medical conditions?

Yes, people with Down syndrome have increased health risks.

Approximately 40% to 60% of infants with Down syndrome have a congenital heart defects.

Low muscle tone is common in people with Down syndrome. This may result in delayed gross motor development like crawling, walking and also constipation and gastro esophageal reflux.

Those with Down syndrome are also at greater risk for childhood leukemia, sleep apnea, thyroid conditions, Alzheimer’s diseases, and diabetes. Many of these conditions are treatable and most people with Down syndrome lead healthy lives.