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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
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
| 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
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.
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.
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