Cytogenetics- Defects

Question 1

What determines the frequency of each aneuploidy

Answer 1

the frequency of each aneuploidy depends on the rate of spontaneous abortion rate.
Non-disjunction is believed to occur at the same rate with all chromosomes… but abortion rates differ. For example: Patau is less frequent than Downs because prenatal mortality is higher with t13 than t21 (more spontaneous abortions occur with t13 than with t21)

Question 2

Down Syndrome
critical region
Characteristics:
Complications

Answer 2

Down Syndrome is caused by trisomy of chromosome 21
Critical Region: region q22.
Characteristics: protruding tongue, furrowed tongue, epicanthal folds, flat nasal bridge, etc.
Complications: Mental retardation, congenital hart disease, alzheimer, immunodeficiency

Question 3

Edwards Syndrome:
critical region:
characteristics:

Answer 3

Edwards Syndrome:
There is no critical region of chromosome 18 for edwards syndrome- the ENTIRE chromosome is required to cause the syndrome
characteristics: Chenched Fists, Overlapping fingers, NO PSYCHOSOCIAL DEVELOPMENT
early death (usually under 1 year)

Question 4

Patau:
characteristics:

Answer 4

Patau= trisomy 13
Characteristics: holoprosencephaly (cleft lip/palate, cyclopsia, CNS abnormalities), microphthalmia
EARLY DEATH (seldom live >1 year)

Question 5

Turner

Characteristics

Answer 5

45, X0 (only one X chromosome)
characteristics: no development of secondary sexual traits, broad “shield” chest, “webbed neck” due to cystic hygroma due to lymphedema, congenital heart disease (aorta coarctation)

Question 6

Klinefelter Syndrome

Answer 6

Klinefelter Syndrome (47, XXY)

Slightly decreased IQ
Gynecomastia
feminized body habitus
hypogonadism
**Inherited equally maternal and paternal

Question 7

How can we detect a chromosomal aberration?

Answer 7

We can detect structural damage to chromosomes using light microscopy

Question 8

Cri du Chat Syndrome

Answer 8

Cri du Chat Syndrome (5p- a deletion of a region near the end of the short arm of chromosome 5)
characterized by a “cat like cry,” severe mental retardation, microcephaly, hypertelorism. in older children you will see an elongated face, less pronounced cry, and a language delay

Question 9

Wolf-Hirshorn Syndrome

Answer 9

Wolf-Hirshorn Syndrome is a deletion in 4p (4p-) you’ll see frontal bossing, cleft lip, heart defects, and an IQ<20

Question 10

Microdeletion Syndromes:

how do we detect them?

Answer 10

Microdeletion Syndromes are submicroscopic deletions inactivating several genes
requires FISH for detection

Question 11

Williams Syndrome

Answer 11

Williams Syndrome is a deletion in 7q11.2. Patients with this deletion will have a wide mouth, full cheeks, a “cocktail personality” learning disabilities, and an UNUSUAL APTITUDE FOR MUSIC

Question 12

DiGeorge Sydrome

Answer 12

DiGeorge Syndrome is a 22 q11.2-22 q11.3 deletion.

CATCH22- Cardiac defect, Abnormal facies, Thymic aplasia, Cleft palate, Hypocalcemia (thymic shadow)