basic knowledge for class 12

2.  Down Syndrome is a genetic condition in
which a person has 47 chromosome instead
of the usual 46.
 1st described by John Langdon Down in 1866
 Formally called mongolism or Mongolian
idiocy.
 Occurs in approximately 1 in every 800 live
births

3.  Down syndrome is usually caused by an error
in cell division called nondisjunction.
 Women over 45years of age are about 20
times more likely to give birth to a child with
Down syndrome

4.  1. Trisomy 21(nondisjunction) is caused by a faulty cell
divison that results in the baby having three 21
chromosomes instead of two. Prior to or at
conception, a pair of 21 chromosome in either the egg
or sperm fails to separate properly. The extra
chromosome is replicated in every cell of the body.
95% of all people with Down syndrome have trisomy
21.

5.  2. About 4% of those with Down
Syndrome are due to Robertsonian
translocation.

7.  3. Mosaicism occurs when non-
disjunction of chromosome 21 take
place in one of the initial cell divisions
after fertilization. When this happens
there is a mixture of 2 types of cells-
some containing 46 chromosome and
some with 47.The cells with 47
chromosome contain an extra 21st
chromosome.
 It occurs in only 1 to 2 percent of all
cases of Down Syndrome.

9.  Common physical signs include-
Decreased muscle tone at birth, flattened
nose,small ears,small mouth,upward slanting
eyes,short hands with short fingers.
Children may also have delayed mental and
social development.
As children with Down syndrome grow and
become aware of their limitations,they may
also feel frustration and anger

10.  There is no specific treatment for Down
syndrome.
 Behavioral training can help people with
Down syndrome and their families deal with
the frustration, anger, and compulsive
behavior that often occur. Parents and
caregivers should learn to help a person with
Down syndrome deal with frustration. At the
same time, it is important to encourage
independence.

11.  Experts recommend genetic counseling for
persons with a family history of Down syndrome
who wish to have a baby.
 A woman's risk of having a child with Down
syndrome increases as she gets older. The risk is
significantly higher among women age 35 and
older.
 Couples who already have a baby with Down
syndrome have an increased risk of having
another baby with the condition.
 Tests such as nuchal translucency ultrasound,
amniocentesis, or chorionic villus sampling can
be done on a fetus during the first few months of
pregnancy to check for Down syndrome.