What is Down Syndrome?

Question

What is Down syndrome? What is the outlook for an infant that is born with Down Syndrome? How can the doctors determine that a baby will be born with Down Syndrome? Is there a cure? What is the chance of having a baby with Down Syndrome? What about the translocation type?

Answer

An amniocenteses is the prenatal procedure to diagnose Down Syndrome. A chromosome test can be done after birth.

Down syndrome (DS) is a genetic disorder that is caused by an extra chromosome 21 that is present in all or some of the individual's cells. There are three types of chromosome abnormalities in Down syndrome. The first is called trisomy 21 and is the most common form of DS. With trisomy 21, the individual has an extra chromosome 21, which results in a total of 47 chromosomes in each cell rather than the typical 46. The second is called mosaicism and is the least common form of DS. In this case, only some of the cells contain 47 chromosomes, while the other cells contain an accurate 46. The third type is called translocation where the extra chromosome attaches (or translocates) to a different chromosome, such as 14 or 22.

The additional chromosome is almost always the result of faulty cell division, in either the egg or sperm, resulting in 3 chromosome 21s (2 from the egg and 1 from the sperm, or vice-versa). Though the extra chromosome could come from either the father or the mother, only 5% of the cases have been traced to the father. Women age 35 years and older have a significantly increased chance of having a child with DS, however, 80% of children born with DS are actually born to mothers under the age of 35 years due to higher fertility rates.

DS is one of the most common chromosome abnormalities. It is estimated that the incidence is between 1 in 800 to 1,000 live births. There are approximately 350,000 individuals in the United States with DS. It occurs in all racial, ethnic, and socioeconomic groups. Recent research shows that slightly more males than females are born with DS in comparison with the general population.

Down syndrome was first accurately described in 1866 by an English physician named John Langdon Down. Then, in 1959, a French physician named Jerome Lejeune identified Down syndrome as a chromosome anomaly. It was Lejeune who observed 47 chromosomes in individuals with DS, rather than 46 chromosomes.

The cause of DS is not known, however, some experts believe that hormonal abnormalities, x-rays, viral infections, immunological problems, or genetic predisposition may be the cause of improper cell division, resulting in the syndrome. What is known, however, is that the extra chromosome 21 causes an extra dose of some proteins, which causes the typical features of the syndrome. In addition, it should be noted that DS is not the result of something that either parent did or did not do.

Features and Characteristics

There are many physical characteristics that are associated with DS. Not every individual has all the characteristics, however, the following is a list of the most common traits:

	Low muscle tone
	Flat facial profile (depressed nasal bridge and small nose)
	Flattening of the back of the head
	Small hands and feet
	An upward slant of the eyes
	An abnormal shape of the ear
	A single deep crease across the center of the palm
	An excessive ability to extend the joints
	Fifth finger has one flexion furrow instead of two
	Small skin folds on the inner corner of the eyes
	Excessive space between large and second toe
	Enlargement of tongue in relation to the size of the mouth
	Mental retardation (can range from very mild to severe, however, is typically mild to moderate)
	Speech delays
	Short stature

In addition to the common characteristics, a child with DS may also have the following medical issues:

	Congenital heart defects
	Increased susceptibility to infection
	Respiratory problems
	Obstructed digestive tracts
	Hearing deficits
	Eye problems such as cataracts and strabismus
	Failure to thrive in infancy and obesity in adolescence
	Thyroid dysfunctions
	Skeletal problems (hip dislocations, atlantoaxial instability)
	Increased risk of developing Alzheimer's disease (over age 35) and leukemia

Diagnosis

Generally, when a child is born with Down syndrome, the appearance of the child is the first indication that he or she may have the disorder. Therefore, a chromosome analysis is conducted which looks for three chromosome 21s or variants as described above. It can also be diagnosed prenatally by either an amniocentesis or chorionic villus sampling.

Treatment

There is no cure for DS, however, early intervention programs, preschools, and integrated education can be very beneficial for the child with DS. With the proper education, many children with DS will learn to read, write, and participate in school activities. In addition to receiving an early education, children with DS may benefit from several therapies as well. Due to the delays in speech that are commonly seen in children with down syndrome, speech therapy is beneficial. The speech pathologist should emphasize adequate development of oral muscles used in feeding and speech articulation, and to focus on developing expressive and receptive skills to enhance communicative functioning. Due to the low tone found in children with DS, physical therapy may be useful in improving gross motor skills such as sitting and walking and improving postural alignment. Finally, children with DS may also benefit from occupational therapy to develop fine-motor skills, self help skills, upper extremity strength, and coordination.

What to Expect

Children with DS can usually do what "typical" children can do, such as walk, talk, play, dress themselves, potty train, etc., however, they generally do these things later than other children. Individuals with Down syndrome should be a part of the community; they strive to accomplish goals just like everyone else. They go to school, have jobs and enjoy leisure activities. Organizations, (i.e., banks, corporations, restaurants, entertainment firms, and computer organizations) actively seek young adults with DS for employment. People with DS bring to their jobs enthusiasm, reliability, and dedication.

Many adults with DS form relationships with others and some even marry. Women with Down syndrome are fertile and can have children; men are believed to be sterile. The life expectancy of an individual with Down syndrome is 55 years.

If you are interested in meeting other parents and individuals who are involved in raising a child with Down syndrome, the following Internet discussion groups are available:

	Down Syndrome List - Send an e-mail to leave the subject field blank, and in the body of the e-mail type the words "subscribe down-syn" (without the quotes), followed by your first and last name. You will then receive a confirmation.
	http://www.specialchild.com/disorder.html

I also have a case study about Cameron's development. Cameron was born with Down Syndrome and is now the middle child in her family. In the Case in Progress archive you can read about her birth, open heart surgery , and her developmental milestones. You might be interested in reading about her and following her progress as she approaches her seconds birthday.

There are many wonderful books for children and families. Here are some that I recommend. You can see a more complete list in the Recommended Reading area.