What is Down syndrome?
Down syndrome (sometimes called Down’s syndrome) is a condition in which a child is born with an extra copy of their 21st chromosome — hence its other name, trisomy 21. This causes physical and mental developmental delays and disabilities.
What causes Down syndrome?
In all cases of reproduction, both parents pass their genes on to their children. These genes are carried in chromosomes. When the baby’s cells develop, each cell is supposed to receive 23 pairs of chromosomes, for 46 chromosomes total. Half of the chromosomes are from the mother, and half are from the father.
In children with Down syndrome, one of the chromosomes doesn’t separate properly. The baby ends up with three copies, or an extra partial copy, of chromosome 21, instead of two. This extra chromosome causes problems as the brain and physical features develop.
Types of Down syndrome
There are three types of Down syndrome:
- Trisomy 21
Trisomy 21 means there’s an extra copy of chromosome 21 in every cell. This is the most common form of Down syndrome.
Mosaicism occurs when a child is born with an extra chromosome in some but not all of their cells. People with mosaic Down syndrome tend to have fewer symptoms than those with trisomy 21.
In this type of Down syndrome, children have only an extra part of chromosome 21. There are 46 total chromosomes. However, one of them has an extra piece of chromosome 21 attached.
Symptoms of Down syndrome
At birth, babies with Down syndrome usually have certain characteristic signs, including:
• Flat facial features
• Small head and ears
• Short neck
• Bulging tongue
• Eyes that slant upward
• Atypically shaped ears
• Poor muscle tone
An infant with Down syndrome can be born an average size, but will develop more slowly than a child without the condition.
These may include:
• Congenital heart defects
• Hearing loss
• Poor vision
• Hip problems, such as dislocations
• Sleep apnea (interrupted breathing during sleep)
• Dementia (thought and memory problems)
Screening for Down Syndrome during pregnancy
Screening for Down syndrome is offered as a routine part of prenatal care in the United States. If you’re a woman over 35, your baby’s father is over 40, or there’s a family history of Down syndrome, you may want to get an evaluation.
Additional prenatal tests
Your doctor may order additional tests to detect Down syndrome in your baby. These may include:
• Chorionic villus sampling (CVS).
• Percutaneous umbilical blood sampling (PUBS, or cordocentesis).
Tests at birth
At birth, your doctor will:
• Perform a physical examination of your baby
• Order a blood test called a karyotype to confirm Down Syndrome
Treating Down syndrome
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. School is an important part of the life of a child with Down syndrome, regardless of intellectual ability. Public and private schools support people with Down syndrome and their families with integrated classrooms and special education opportunities.