What is Trisomy 21ā?
Down syndrome is a condition in which a person has an extra chromosome. Chromosomes are small āpackagesā of genes in the body. They determine how a babyās body forms during pregnancy and how the babyās 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 ātrisomy.ā Down syndrome is also referred to as Trisomy 21. This extra copy changes how the babyās body and brain develop, which can cause both mental and physical challenges for the baby.
Even though people with Down syndrome might act and look similar, each person has different abilities. People with Down syndrome usually have an IQ (a measure of intelligence) in the mildly-to-moderately low range and are slower to speak than other children.
Content provided by the Centers for Disease Control and Prevention (CDC). For information and references about trisomy 21, please visit Facts about Down Syndromeā | CDC ā.
Rates of Trisomy 21: 2018ā2020ā
Overallā
By Age
ā24 and under
|
7.6
|
ā25ā29
|
6.2
|
ā30ā34
|
11.6
|
ā35ā39
|
33.2
|
ā40 and over
|
109.9
|
āBy Race and Ethnicity
āAmerican Indian/Alaskan Native, Native Hawaiian/Pacific Islander, Other/Non-Hispanic
|
ā25.7
|
āAsian/Non-Hispanic
|
7.7
|
āBlack/Non-Hispanic
|
11.9
|
āHispanic
|
19.1
|
White/Non-Hispanic
|
11.5
|
*Per 10,000 live births
Data Source: California Birth Defects Monitoring Program Registry, 2018āā2020, California 10-County Catchment Area (Fresno, Kern, Kings, Madera, Merced, Orange, San Diego, San Joaquin, Stanislaus, and Tulare)
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