Approximately 1 out of 800 babies that are born in the United States have Down syndrome. Down syndrome is a disorder that causes developmental delays, mental retardation and other mental and physical conditions. It is a genetic disorder that occurs as a result of extra genetic material being present during fetal development. There are varying levels of Down syndrome, causing a wide range in the severity of symptoms.
It is generally easy to recognize Down syndrome in children because the condition presents with very distinct facial features. Most children with Down syndrome will have the following facial appearance:
- Smaller than average head
- Shorter than average neck
- Flattened facial features
- A tongue that protrudes form the mouth
- Eyes that slant upward
- Unusually shaped ears
Other physical characteristics that may be present in children with Down syndrome include:
- Short hands with only one crease in the palm
- Shorter than average fingers
- Poor muscle tone
- Excessive flexibility
Infants may not have these features immediately, and they often are of average size at birth. Down syndrome may be suspected if certain factors are present. It is common for infants with Down syndrome to:
- Grow slower than average
- Remain shorter than other babies of similar age
- Not reach developmental milestones, such as crawling and sitting, until nearly twice the age of children without Down syndrome
Under normal circumstances, human cells consist of 23 pairs of chromosomes. In each pair of chromosomes, one comes from the father and one comes from the mother. During fetal development, the fetus inherits 23 chromosomes from the mother and 23 chromosomes from the father. Down syndrome occurs when an extra chromosome is passed onto the fetus. There are 3 genetic variations that can cause the abnormal cell division that causes Down syndrome. The 3 variations are:
- Trisomy 21. This is the most common cause of Down syndrome, responsible for approximately 90 percent of cases. Instead of having 2 copies of chromosome 21, children who are born with trisomy 21 have 3 copies in all of their cells. This type of Down syndrome occurs as a result of abnormal cell division that occurs during the developmental stages of sperm or egg formation.
- Mosaic Down syndrome. This is a rare form of Down syndrome. Similar to trisomy 21, children with this type of Down syndrome have an extra copy of chromosome 21; however, it is not present in all of the cells, only some of them. This type of Down syndrome occurs as a result of abnormal cell division that occurs after the egg has been fertilized by the sperm.
- Translocation Down syndrome. This is the most uncommon form of Down syndrome, occurring in approximately 4 percent of children with Down syndrome. This type of Down syndrome occurs when a portion of chromosome 21 attaches itself to another chromosome, causing children to have the regular copies of chromosome 21, as well as additional material from chromosome 21. This type of Down syndrome occurs before conception or at the time of conception.
Despite what many people believe, Down syndrome is not an inherited condition. It occurs due to an abnormal cell division that occurs before or during fetal development. However, Translocation Down syndrome can be passed down from a parent to a child. Of the 4 percent of children with Down syndrome who have the Translocation type, only half of them inherit the condition from a parent. One of the parents must be a carrier. If the mother is the carrier, the risk of passing the condition onto the child is double that of the father being the carrier. A parent who is a carrier of this type of Down syndrome has some extra genetic material, but does not show any signs of Down syndrome.
There is no known association between environmental or behavioral factors being a risk for Down syndrome. There are some factors that place parents at a greater risk of having a child with some form of Down syndrome. Risk factors include:
- Advanced maternal age. By the age of 35, a woman’s risk of giving birth to a child with Down syndrome is 1 in 400. By the age of 45, that risk jumps up to 1 in 35. This is because the older a woman is, the greater her chance of having abnormal chromosome division. Although advanced maternal age is a factor, the majority of children with Down syndrome are born to women under 35. This is because more women under the age of 35 are having babies than women over 35.
- Having a child with Down syndrome. If a woman gives birth to a child with Down syndrome, she has a slightly higher risk (approximately 1 percent) of having another child with Down syndrome.
- Being a carrier of Translocation Down syndrome. Either parent can pass the genetic translocation form of Down syndrome to a child. If either the mother or father is a carrier, there is an increased risk.
Women are given the option to screen for Down syndrome as a part of their normal prenatal care. Most obstetricians offer a variety of screening tests throughout the pregnancy. All women are offered these tests, regardless of age. Typical screening tests that are offered during pregnancy include:
- Blood tests
- First trimester ultrasound
- Combined tests (blood and ultrasound)
- Quad screen (checks levels of alpha fetoprotein, estriol, HCG and inhibin A)
These tests cannot identify Down syndrome; they can only identify women who are at an increased risk of having a baby with Down syndrome. A positive result may prompt some women to have more invasive diagnostic tests that can give a conclusive result. Additional, more invasive diagnostic tests include:
- Chorionic villus sampling (CVS)
- Percutaneous umbilical blood sampling (PUBS)
- Analysis of mother’s blood to check for circulating fetal (not widely available yet)
After birth, Down syndrome can be diagnosed by the baby’s appearance if it is recognized. If some of the characteristics are present at birth, a test of the baby’s chromosomes will be ordered to confirm the diagnosis of Down syndrome.
Early intervention programs are recommended for children with Down syndrome. These are specialized programs that work with Down syndrome children from a very early age to help with sensory integration, motor skills and cognitive learning. Programs vary, but generally include treatment form physical therapists, occupational therapists and special education instructors.
Children with Down syndrome may have physical conditions that require additional treatment. Additional treatment options include:
- Pediatric cardiologist
- Pediatric gastroenterologist
- Pediatric endocrinologist
- Pediatric neurologist
- Physical therapist
- Occupational therapist
- Developmental pediatrician
- Speech pathologist
Parents of children with Down syndrome often experience a range of emotions. After a diagnosis is given, many parents struggle with feelings of anger, fear, guilt and sorrow. Many parents are apprehensive about what to expect and they worry about the developmental health of their child. They may question their ability to care for a child with Down syndrome.
To combat these feelings, it is important for parents to learn all they can about Down syndrome and seek out support services. Parents are encouraged to start building a team of specialists as soon as possible, including doctors, therapists, teachers, counselors, support groups and other parents of Down syndrome children.
Parents should remember that many children with Down syndrome have fulfilling childhoods and a high quality of life. They often go to mainstream schools, are able to read and write, hold a job and can have a life expectancy of 50+ years.