Few MCQs on Down's Syndrome

As 21 March is World Down Syndrome Day, lets solve some MCQs related to Down's Syndrome.

1. The following conditions are caused by non-disjunction except:

A. Phenylketonuria
B. Down's syndrome
C. Patau's syndrome
D. Edward's syndrome

2. A newborn female child presenting with hypoplastic left heart syndrome was found to have 45XO chromosomes. The diagnosis is:

A) Klinefelter syndrome
B) Down’s syndrome
C) Turner syndrome
D) Robertsonian translocations

3. All of the following are single gene disorders except:

A) Klinefelter syndrome
B) Marfan syndrome
C) Cystic fibrosis
D) Hemophilia

4. Choose an option that does not represent chromosomal disorder:

A) Klinefelter syndrome
B) Down Syndrome
C) Turner syndrome
D) Duchenne muscular dystrophy

5. What is the most common viable aneuploidy (abnormal number of chromosomes) in humans?

A) Klinefelter syndrome
B) Down syndrome
C) Edwards syndrome
D) Turner syndrome

6. The commonest mechanism of genetic abnormality in a case of Trisomy 21 is:

A) Nondysjunction in maternal gamete
B) Nondysjunction in paternal gamete
C) Translocation to chromosome 14
D) Translocation to any autosome

7. Chorionic villus sampling is done at what gestation?

A) 6-9 weeks
B) 10-12 weeks
C) 14-20 weeks
D) 14-28 weeks


1. A

Ans: 2- C
45XO represents monosomy X or Turner syndrome. Most commonly observed congenital heart disease are obstructive lesions of the left side of the heart including coarctation of aorta, bicuspid aortic valve and hypoplastic left heart syndrome.
Ans: 3-A
Klinefelter syndrome is a chromosomal disorder in which there is at least one extra X chromosome in the genetic makeup. Thus it is known as the chromosomal disorder and is not a single gene mutation.
Ans: 4- D
Duchenne muscular dystrophy is X- linked recessive condition.
Ans: 5- B
Down syndrome ( Trisomy 21) is the most common autosomal aneuploidy that the infant can servive with. Klinefelter syndrome (at least one extra X chromosome) is the most common sex chromosome aneuploidy. Most cases of Turner syndrome (Monosomy X) result in abortions. Edwards syndrome (trisomy 18) is rare.
Ans: 6- A
Trisomy 21 is caused by a meiotic nondysjunction event most commonly in the ovum. The affected ovum has 24 chromosomes with an extra copy of chromosome 21. When it combines with a normal sperm, the embryo has 47 chromosomes with trisomy 21. Mechanisms mentioned in other options are less common causes of Down syndrome.
Ans: 7- B
Chorionic villus sampling is done after 9 weeks of gestation till 12.5 weeks of gestation. Amniocentesis can be done from about 14 weeks till 20weeks.

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