Down Syndrome
Down syndrome is the most frequent genetic cause of mild to moderate mental retardation with
associated medical problems.  Down syndrome occurs in one out of 800 live births, in all races and
economic groups. Down syndrome is a chromosomal disorder caused by an error in cell division that
results in the presence of an additional third chromosome 21 or "trisomy 21." When the fertilized egg
contains extra material from chromosome number 21, the result is a child with Down syndrome. Named
after John Langdon Down, the first physician to identify the syndrome. This disorder includes a
combination of birth defects; among them are some degree of mental retardation, characteristic facial
features and, often, heart defects, increased infections, problems with vision and hearing, and other
health problems.

Genetics of Down Syndrome

Comprehending why Down syndrome occurs, the structure and function of the human chromosome
must be understood. The human body is made of cells; all cells contain chromosomes, structures that
transmit genetic information. Most cells of the human body contain 23
pairs of chromosomes, half of
which are inherited from each parent. When the reproductive cells, the sperm and ovum, combine at
fertilization, the fertilized egg that results contains 23 chromosome
pairs. Three genetic variations can
cause Down syndrome. In most cases, approximately 92% of the time, Down syndrome is caused by
the presence of an extra chromosome 21 in cells of the individual. When the egg and sperm unite to
form the fertilized egg,
three rather than two chromosomes 21 are present resulting in Down
syndrome.

Down syndrome is not attributable to any behavioral activity of the parents or environmental factors.
Researchers have extensively studied the defects in chromosome 21 that cause Down syndrome. In
88% of cases, the extra copy of chromosome 21 is derived from the mother. In 8% of the cases, the
father provided the extra copy of chromosome 21. In the remaining 2% of the cases, Down syndrome is
due to the forming of 2 cells from one; an error in cell division occurs after fertilization when the sperm
and ovum are joined.

Maternal Age

The incidence of Down syndrome rises with increasing maternal age. Researchers have established
that the likelihood that a reproductive cell will contain an extra copy of chromosome 21 increases
dramatically as a woman ages. However, of the total population, older mothers have fewer babies;
about 75% of babies with Down syndrome are born to younger women because younger women are
more likely to become pregnant. Many specialists recommend that women who become pregnant at
age 35 or older undergo prenatal testing for Down syndrome. The likelihood that a woman under 30
who becomes pregnant will have a baby with Down syndrome is less than 1 in 1,000, but the chance of
having a baby with Down syndrome increases to 1 in 400 for women who become pregnant at age 35
or older, about 25% of babies with Down syndrome are born to women in this age group. The
probability that another child with Down syndrome will be born in a subsequent pregnancy is about 1
percent, regardless of maternal age.

Diagnosis of Down Syndrome

A newborn baby with Down syndrome often has physical features the attending physician will most
likely recognize in the delivery room. These may include a flat facial profile, an upward slant to the eye,
a short neck, abnormally shaped ears, white spots on the iris of the eye (called Brushfield spots), and
a single, deep transverse crease on the palm of the hand. However, a child with Down syndrome may
not possess all of these features; some of these features can even be found in the general population.
To confirm the diagnosis, the doctor will request a blood test called a chromosomal karyotype. This
involves "growing" the cells from the baby's blood for about two weeks, followed by a microscopic
visualization of the chromosomes to determine if extra material from chromosome 21 is present.

Caring for Children with Down Syndrome

When parents are told that their newborn baby has Down syndrome, it is not unusual for them to have
feelings of sadness, disappointment and anxiety. Medical care for infants with Down syndrome should
include the same well-baby care that other babies receive. With the diagnosis of Down syndrome it’s
unknown the intellectual or physical capabilities this child, or any other child, you may have. Children
and adults with Down syndrome have a wide range of abilities. A person with Down syndrome may be
very healthy or they may present unusual and demanding medical and social problems. Every person
with Down syndrome is a unique individual, and not all children  with Down syndrome will develop
medical disorders.

Early Childhood Development

Children with Down syndrome may be developmentally delayed. A child with Down syndrome is often
slow to turn over, sit, stand, and respond. This may be related to the child's poor muscle tone.
Development of speech and language abilities may take longer than expected and may not occur as
fully as parents would like. However, children with Down syndrome do develop the communication skills
they need. Parents should keep in mind that children with Down syndrome have a wide range of
abilities and talents, and each child develops at his or her own particular pace. It may take children with
Down syndrome longer than other children to reach develop- mental milestones, but many of these
milestones will eventually be met.
For more detailed information on Down syndrome please visit:
http://www.nichd.nih.gov

News, resources and scientific information related to Down syndrome:
http://www.nads.org             
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