Name: What is Down Syndrome (Trisomy 21)? Down syndrome (Trisomy 21) Made Easy
Uploaded: 2025-05-09T16:18:47.000Z
Duration: 6 min 49 s
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Down syndrome is a genetic disorder in which a person has an extra chromosome.

Chromosomes are small packages of genes in the body.

They determine how a baby's body forms and functions as it grows during pregnancy and after birth.

Typically, a baby is born with 46 chromosomes.

Babies with Down syndrome have an extra copy of chromosome 21.

A medical term for having an extra copy of a chromosome is a trisomy.

Therefore, Down syndrome is also referred to as trisomy 21.

This extra copy changes how the baby's 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.

Many of the disabilities are lifelong, and they can also shorten life expectancy.

However, people with Down syndrome can live healthy and fulfilling lives.

People with Down syndrome usually have an IQ in the mildly to moderately low range and are slower to speak than other children.

Children and adults with Down syndrome have distinct facial features.

Though not all people with Down syndrome have the same features, some of the more common features include.

A flattened face, especially the bridge of the nose.

A tongue that tends to stick out of the mouth.

Tiny white spots on the iris, colored part of the eye.

A single line across the palm of the hand, palmar crease.

Small pinky fingers that sometimes curve toward the thumb.

Shorter in height as children and adults.

Down syndrome remains the most common chromosomal condition diagnosed in the United States.

Each year, about 6,000 babies born in the United States have Down syndrome.

This means that Down syndrome occurs in about 1 in every 700 babies.

About 95% of people with Down syndrome have trisomy 21.

With this type of Down syndrome, each cell in the body has three separate copies of chromosome 21 instead of the usual two copies.

This type accounts for about 3% of people with Down syndrome.

This occurs when an extra part or a whole extra chromosome 21 is present, but it is or, translocated, to a different chromosome rather than being a separate chromosome 21.

This type affects about 2% of the people with Down syndrome.

For children with mosaic Down syndrome, some of their cells have three copies of chromosome 21, but other cells have the typical two copies of chromosome 21.

Children with mosaic Down syndrome may have the same features as other children with Down syndrome.

However, they may have fewer features of the condition due to the presence of some cells with a typical number of chromosomes.

There are two basic types of tests available to detect Down syndrome during pregnancy, screening tests and diagnostic tests.

A screening test can tell a woman and her healthcare provider whether her pregnancy has a lower or higher chance of having Down syndrome.

Screening tests do not provide an absolute diagnosis, but they are safer for the mother and the developing baby.

Diagnostic tests can typically detect whether or not a baby will have Down syndrome, but they can be riskier for the mother and developing baby.

Neither screening nor diagnostic tests can predict the full impact of Down syndrome on a baby, no one can predict this.

Screening tests often include a combination of a blood test, which measures the amount of various substances in the mother's blood, example, MSAFP, triple screen, quad screen, and an ultrasound, which creates a picture of the baby.

During an ultrasound, one of the things the technician looks at is the fluid behind the baby's neck.

Extra fluid in this region could indicate a genetic problem.

These screening tests can help determine the baby's risk of Down syndrome.

Diagnostic tests are usually performed after a positive screening test in order to confirm a Down syndrome diagnosis.

Chorionic villa sampling, CVS, examines material from the placenta.

Amniocentesis, examines the amniotic fluid.

Percutaneous umbilical blood sampling, PUBS, examines blood from the umbilical cord.

These tests look for changes in the chromosomes that would indicate a Down syndrome diagnosis.

Some people with Down syndrome might have one or more major birth defects or other medical problems.

There's no cure for Down syndrome, but there's a wide variety of support and educational programs that can help both people with the condition and their families.

In these programs, special education teachers and therapists will help your child learn.

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What is Down Syndrome (Trisomy 21)? Down syndrome (Trisomy 21) Made Easy

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