Lecture 9: Cytogenetics I

Question 1

What is the karyotype for Trisomy 13?

Answer 1

47,XX,+13 (female)

47,XY,+13 (male)

Question 2

What is the eponym for Trisomy 13?

Answer 2

Patau

Question 3

What are the clinical features of Trisomy 13?

Answer 3

• Midline deformations
• Microcephaly
• CHD
• Scalp defects (cutis aplasia)
• Holoprosencephaly
• Microphtalmia
• Cleft palate
• Polydactyly
• Renal anomalies

Question 4

List all three trisomies in order of their incidence rates.

Answer 4

Trisomy 13: 1-2 in 10,000 (low)

Trisomy 18: 1-2 in 6,000 (medium)

Trisomy 21: 1 in 700 (high)

Question 5

What is the prognosis for Trisomy 13?

Answer 5

Poor, 95% die in the first six months.

Question 6

What is the karyotype for Trisomy 18?

Answer 6

47,XX,+18 (female)

47,XY,+18 (male)

Question 7

What is the alternative name for Trisomy 18?

Answer 7

Edwards

Question 8

What are the clinical features of Trisomy 18?

Answer 8

• Small size
• Small head circumference
• Congenital heart defects
• Overlapping fingers
• Rocker bottom feet

Question 9

What is the prognosis for Trisomy 18?

Answer 9

Poor, 95% die within 12 months.

Question 10

What is the karyotype for Trisomy 21?

Answer 10

47,XX,+21 (female)

47,XY,+21 (male)

Question 11

What is the alternative name for Trisomy 21?

Answer 11

Down

Question 12

What are the clinical features of Trisomy 21?

Answer 12

• Flat facial profile
• Upslanted palpebral fissures
• Anomalous auricles
• Nuchal skin fold
• Single palmar crease
• Clinodactyly
• Hypotonia
• Hyperflexible joints
• Intellectual Disability
• Sandle gap

Question 13

What is the prognosis for Trisomy 21?

Answer 13

Live into 50s/60s.

Question 14

What is the karyotype of Turner Syndrome?

Answer 14

45,X

Question 15

What are the clinical features of Turner Syndrome?

Answer 15

• Lymphedema in infancy
• Bicuspid aortic valve
• Coarctation of aorta
• Short stature
• Gonadal regression (streak ovaries)
• Low posterior hairline
• Webbed neck
• Widely spaced nipples
• Horseshoe kidney
• Cubitus valgus of elbow

Question 16

What is the prognosis for Turner Syndrome?

Answer 16

Good, however the vast majority are lost as SABs. Only few live.

Question 17

What is the karyotype for Klinefelter Syndrome?

Answer 17

47,XXY

Question 18

What are the clinical features of Klinefelter Syndrome?

Answer 18

• Tall stature
• Long limbs
• Learning disabilities
• Gynecomastia (post-puberty)
• Small testicles
• Infertility

Question 19

What are the clinical features of 47,XXY males?

Answer 19

• Normal physical appearance
• Stature is above average
• Intelligence is usually normal
• IQ scores are often 10-15 points below that of siblings
• Emotional immaturity and impulsive behavior

Question 20

What are the clinical features of 47,XXX females?

Answer 20

• Physical appearance is usually normal
• IQ is generally 10-15 points below that of siblings
• Verbal language is often delayed
• Women with 47,XXX karyotypes usually have normal fertility but there is an increased incidence of fertility problems compared to the normal population.

Question 21

Monosomy

Answer 21

Occurs from non-disjunction; the cell is shorted one chromosome.

Question 22

Trisomy

Answer 22

Occurs from non-disjunction; the cell gains a chromosome.

Question 23

When does heterodisomy (UPD) occur?

Answer 23

M1 block

Question 24

When does isodisomy (UPD) occur?

Answer 24

M2 block