Down Syndrome


What is it?

A syndrome that causes recognizable physical characteristics and limited intellectual endowment, due to the presence of an extra chromosome 21.

Cause?

It is not known what actually causes Down syndrome. Some professionals believe that hormonal abnormalities, X-rays, viral infections, immunologic problems, or genetic predisposition may be the cause of the improper cell division that results in Down syndrome.

It has been known for some time that the risk of having a child with Down syndrome increases with advancing age of the mother; i.e., the older the mother, the greater the possibility that she may have a child with Down syndrome. However, most babies with Down syndrome (more than 85 percent) are born to mothers younger than 35 years. Some investigators reported that older fathers may also be at an increased risk of having a child with Down syndrome.

It is well known that the extra chromosome in trisomy 21 could either originate in the mother or the father. Most often, however, the extra chromosome is coming from the mother.

Characteristics:

Contrary to popular belief, not every child with Down syndrome has all the characteristics - some may only have a few, and others may show most of the signs of Down syndrome.
Some of the physical features include:
  • flattening of the back of the head
  • slanting of the eyelids
  • small skin folds at the inner corner of the eyes
  • depressed nasal bridge
  • slightly smaller ears
  • small mouth
  • decreased muscle tone
  • loose ligaments
  • small hands and feet
About 50% of all children with DS have one line across the palm, and there is often a gap between the first and second toes. The physical features observed in children with Down syndrome (and there are many more than described above) usually do not cause any disability in the child.

Possible Health Concerns:

  • 60% - 80% of children with Down syndrome have hearing deficits.
  • 40% - 45% of children with Down syndrome have congenital heart disease. Many of these children will have to undergo cardiac surgery and often will need long term care by a pediatric cardiologist.
  • Intestinal abnormalities occur at a higher frequency. For example, a blockage of the food pipe (esophagus), small bowel (duodenum), and at the anus are not uncommon in infants with Down syndrome.
  • Eye problems - 3% of infants with Down syndrome have cataracts; others include cross-eye (strabismus), near-sightedness, far-sightedness.
  • Some children with Down syndrome, in particular those with severe heart disease often fail to thrive in infancy. On the other hand, obesity is often noted during adolescence and early adulthood.
  • Thyroid dysfunctions - between 15% and 20% children with Down syndrome have hypothyroidism.
  • Skeletal problems including kneecap subluxation (incomplete or partial dislocation), hip dislocation, and atlantoaxial instability. The latter condition occurs when the first two neck bones are not well aligned because of the presence of loose ligaments.
  • Other important medical aspects include immunologic concerns, leukemia, Alzheimer disease, seizure disorders, sleep apnea and skin disorders.

Incidence:

The estimated incidence of Down syndrome is between 1 in 1,000 to 1 in 1,100 live births. Each year approximately 3,000 to 5,000 children are born with this chromosome disorder. It is believed there are about 250,000 families in the United States who are affected by Down syndrome.

Things to note:

Children with Down syndrome are usually smaller, and their physical and mental developments are slower, than youngsters who do not have Down syndrome. The majority of children with Down syndrome function in the mild to moderate range of cognitive disability. However, some children are not mentally delayed at all; they may function in the borderline to low average range; while others may have a severe mental delay. There is a wide variation in mental abilities and developmental progress in children with Down syndrome. Also, their motor development is slow; and instead of walking by 12 to 14 months as other children do, children with Down syndrome usually learn to walk between 15 to 36 months. Language development is also markedly delayed.

It is important to note that a caring and enriching home environment, early intervention, and integrated education efforts will have a positive influence on the child’s development.

Info taken from the Arc's FAQ on Down Syndrome website.


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