Mutational disorders,mutational diseases

1. Down syndrome
Mutational diseases
Mahedi hassn Azan

2. Down Syndrome
(Trisomy 21)
What are trisomies?
Answer-
The term trisomy is used to describe the presence of
three chromosomes, rather than the usual matched
pair of chromosomes. For example, if a baby is born
with three #21 chromosomes, rather than the usual
pair, then the baby would be said to have "trisomy
21." Trisomy 21 is also known as Down syndrome.
Other examples of trisomy include syndromes like
trisomy 18 and trisomy 13. Again, trisomy 18 or
trisomy 13 simply means the child has three copies
of the #18 chromosome (or of the #13 chromosome)
present in each cell of the body, rather than the usual
pair.

3. What is Down syndrome?
Answer-
Down syndrome is a genetic disorder that involves
birth defects, intellectual disabilities, characteristic
facial features. Additionally, it often involves heart
defects, visual and hearing impairments, and other
health problems. The severity of all of these
problems varies greatly among affected individuals.
Down syndrome is one of the most common genetic
birth defects, affecting approximately one in about
800 babies. In this country, around 250,000
individuals have Down syndrome. Life expectancy
among adults with Down syndrome is about 60 years,
though average lifespan varies.
The term Down syndrome comes from Dr. Langdon
Down, the doctor who first described the collection of
physical symptoms in 1866. It was not until 1959 that
the cause of Down syndrome (the presence of an
extra #21 chromosome) was identified.

4. What causes Down syndrome?
ANswer-
Normally in reproduction, the egg cell of the mother
and the sperm cell of the father start out with the
usual number of 46 chromosomes. The egg and
sperm cells both undergo a cell division in which the
46 chromosomes are divided in half, so that both the
egg and the sperm cells will have 23 chromosomes
each. When a sperm with 23 chromosomes fertilizes
an egg with 23 chromosomes, the baby will have a
complete set of 46 chromosomes, half from the father
and half from the mother.

5. Sometimes, an error occurs when the 46
chromosomes are being divided in half, and an egg or
sperm cell keeps both copies of the #21 chromosome
instead of just one copy. If this egg or sperm is
fertilized, then the baby will have three copies of the
#21 chromosome, which is called trisomy 21, or
Down syndrome. The features of Down syndrome are
caused by that extra copy of chromosome #21 being
in every cell in the body.
Most cases of Down syndrome are caused by trisomy
21. Occasionally, the extra chromosome #21 or a
portion of it is attached to another chromosome in
the egg or sperm; this may cause "translocation Down
syndrome." This is the only form of Down syndrome
that may be inherited from a parent. Some parents
have a rearrangement called a balanced
translocation, in which the

6. #21 chromosome is attached to another
chromosome, but it does not affect their own health.
Rarely, another form called "mosaic Down syndrome"
may occur when an error in cell division happens
after fertilization. These individuals have some cells
with an extra chromosome #21 (47 chromosomes
total), and other cells have the usual number (46
total).

7. What does a child with Down
syndrome look like?
Answer-
A child with Down syndrome may have eyes that slant
upward and small ears that may fold over slightly at
the top. The child's mouth may be small, making the
tongue appear large. The child's nose also may be
small, with a flattened nasal bridge. Some babies with
Down syndrome have a short neck and small hands
with short fingers. Rather than having three "creases"
in the palm of the hand, a child with Down syndrome
usually has one single crease that goes straight
across the palm, and a second crease that curves
down by the thumb. The child or adult with Down
syndrome is often short and has unusual looseness
of the joints. Most children with Down syndrome will
have some, but not all, of these features.

8. How significant is the degree of
intellectual disability that
accompanies Down syndrome?
Answer-
The degree of intellectual disability that accompanies
Down syndrome varies widely. It ranges from mild to
moderate to severe. However, most intellectual
disability falls within the mild to moderate range.
There is no way to predict the mental development of
a child with Down syndrome based on their physical
features.

9. What disabilities does a child with
Down syndrome have?
Answer-
Children with Down syndrome can usually do most
things that any young child can do, such as walking,
talking, dressing, and being toilet trained. However,
they generally do these things later than other
children. The exact age that these developmental
milestones will be achieved cannot be predicted.
However, early intervention programs, beginning in
infancy, can help these children achieve their
individual potential.

10. Can Down syndrome be cured or
prevented?
Answer-
There is no cure for Down syndrome. Doctors are not
certain how to prevent the chromosomal error that
causes Down syndrome. To date, there is no reason
to believe that a parent could have done anything to
cause or prevent the birth of a baby with Down
syndrome. However, a recent study suggests that
some women who have had a baby with Down
syndrome had an abnormality in how their body
metabolizes, or processes, the B vitamin folic acid. If
confirmed, this finding may provide yet another
reason why all women who might become pregnant
should take a daily multivitamin containing 400
micrograms of folic acid. This has been shown to
reduce the risk for certain birth defects of the brain
and spinal cord.

11. Some people claim that various high-dose vitamins
given to children with Down syndrome will improve
the mental performance and lessen the degree of
intellectual disability. To date, however, no medical
studies have proved that this actually works. It is
important for new families to talk with their physician,
other families, and national Down syndrome support
agencies to learn what to expect with Down syndrome
and to learn about things that may be helpful in
raising a child with Down syndrome.