Chromosomal Abnormalities

Question 1

List how and when samples of DNA can be obtained for karyotyping.

Answer 1

1. Bone marrow biopsy - 0-1 day
2. Blood sample and culture - 2-3 days
3. Chorionic villus sampling - 7-21 days
4. Amniocentesis - 7-21
5. Solid tissue biopsy and culture (eg. skin) - 7-21

Question 2

List numerical chromosomal abnormalities.

Answer 2

1. Aneuploidy - number of chromosomes that is not a multiple of the haploid no. Monosomy, trisomy
2. Polyploidy - multiple of haploid no. Triploidy, tetraploidy

Question 3

What are some indications for karyotyping?

Answer 3

1. Prenatal screening
   - abnormal ultrasound
   - screening for Down syndrome esp if maternal age > 35
   - FHx of chromosomal abnormalities
2. Recurrent miscarriage
3. Birth deformity, malformation, developmental issues
4. Infertility

Question 4

List symptoms of Down syndrome.

Answer 4

1. Mild-mod intellectual impairment
2. Hearing problems
3. Eye problems - cataracts
4. Infertility - makes, reduced in females
5. Congenital heart disease
6. GI - no nerves in colon, constipation

Question 5

Symptoms of Edwards Syndrome.

Answer 5

1. Low set ears
2. Low hairline
3. Webbed neck
4. Broad chest
5. No intellectual impairment
6. Hearing problems

Question 6

Syx of Patau Syndrome.

Answer 6

1. Lower IQ
2. Polydactyly is common
3. Cleft lip
4. Small eyes, close set eyes
5. Microcephaly

Question 7

List sex chromosome aneuploidies.

Answer 7

1. Turner - 45,X
2. Kleinfelter’s - 47,XXY
3. Triple X - 47,XXX
4. 47,XYY

Question 8

What is a Barr body?

Answer 8

Inactivated X chromosome in the periphery of nucleus.

Question 9

Why is having only one X chromosome in Turner’s syndrome a problem?

Answer 9

X and Y chromosomes have pseudo-autosomal regions (PAR) at the ends of the chromosomes that are the same on the X and the Y. So having only one sex chromosome means the individual is monosomic for those genes.

Question 10

How can chromosomes be visualized?

Answer 10

1. Ideograms
2. FISH using probes
3. mFISH