A Life Worth Celebrating the Extra

What is Down syndrome?

Introduction

In every cell in the human body there is a nucleus, where genetic material is stored in genes. Genes carry the codes responsible for all of our inherited traits and are grouped along rod-like structures called chromosomes. Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.

This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. A few of the common physical traits of Down syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm – although each person with Down syndrome is a unique individual and may possess these characteristics to different degrees, or not at all.

How common is Down syndrome?

According to the Centers for Disease Control and Prevention, approximately one in every 772 babies in the United States is born with Down syndrome, making Down syndrome the most common chromosomal condition. About 5,100 babies with Down syndrome are born in the United States each year. (De Graaf et al., 2022).

There are 3 different types of Down syndrome.

Trisomy 21 (Nondisjunction)

Down syndrome is usually caused by an error in cell division called “nondisjunction.” Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. This type of Down syndrome, which accounts for 95% of cases, is called trisomy 21.

Mosaicism

Mosaicism (or mosaic Down syndrome) is diagnosed when there is a mixture of two types of cells, some containing the usual 46 chromosomes and some containing 47. Those cells with 47 chromosomes contain an extra chromosome 21.

Mosaicism is the least common form of Down syndrome and accounts for only about 2% of all cases of Down syndrome (Facts about Down syndrome, 2021). Research has indicated that individuals with mosaic Down syndrome may have fewer characteristics of Down syndrome than those with other types of Down syndrome. However, broad generalizations are not possible due to the wide range of abilities people with Down syndrome possess.

Translocation

In translocation, which accounts for about 3% of cases of Down syndrome, the total number of chromosomes in the cells remains 46; however, an additional full or partial copy of chromosome 21 attaches to another chromosome, usually chromosome 14 (Facts and Down syndrome, 2021). The presence of the extra full or partial chromosome 21 causes the characteristics of Down syndrome.

Preferred Language Guide

Use this language when referring to Down syndrome and people who have Down syndrome:

• People with Down syndrome should always be referred to as people first.
• Instead of “a Down syndrome child,” it should be “a child with Down syndrome.” Also avoid “Down’s child” and describing the condition as “Down’s,” as in, “He has Down’s.”
• Down syndrome is a condition or a syndrome, not a disease.
• People “have” Down syndrome, they do not “suffer from” it and are not “afflicted by” it.
• “Typically developing” or “typical” is preferred over “normal.”
• “Intellectual disability” or “cognitive disability” has replaced “mental retardation” as the appropriate term.
• Gulf Coast Down Syndrome Society strongly condemns the use of the word “retarded” in any derogatory context. Using this word is hurtful and suggests that people with disabilities are not competent.

Gulf Coast Down Syndrome Society uses the proper spelling of “Down syndrome”. The physician who characterized “Down syndrome” was John Langdon Down. His name is not possessive and, therefore, an “apostrophe s” is not needed. The language and proper uses can be found with both in books and other literature, but the updated material forego adding the “s”.

Provided by: National Down Syndrome Society - NDSS

For more information, please visit: https://ndss.org/about

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