Lect 12 - Genetic Screening and Counseling

Question 1

What is the difference between targeted and population screening?

Answer 1

Targeted screening is more specific screening in ethnic groups, possible high risk carriers, etc. Population screening is prenatal/newborn screening for common genetic disorders found in general population.

Question 2

What are four major genetic disorders tested for prenatally?

Answer 2

1) Trisomy 21 (Down syndrome)
2) Trisomy 18 (Edward syndrome)
3) Trisomy 13 (Patau syndrome)
4) Neural tube defects

Question 3

What are two non-invasive prenatal genetic screening modalities?

Answer 3

1) maternal serum

2) ultrasound

Question 4

What is looked for on ultrasound to diagnose neural tube defects?

Answer 4

Nuchal translucency

Question 5

What are two invasive prenatal genetic screens?

Answer 5

1) amniocentesis

2) Chorionic Villus sampling

Question 6

What are the two proteins sampled for in the first trimester in the maternal serum?

Answer 6

1) PAPP-A

2) beta-hCG

Question 7

What are the four proteins sampled for in the second trimester in the maternal serum?

Answer 7

1) alpha-fetoprotein
2) estriol
3) beta-hCG
4) inhibin A

Question 8

What two neural tube defects is AFP increased in? What disorder is it decreased?

Answer 8

Increased in open spina bifida and anencephaly. Decreased in Down syndrome.

Question 9

There is an increase in the amount of cfDNA (cell free DNA) or fetal DNA fragments in which genetic disorder?

Answer 9

Down Syndrome

Question 10

What are some features seen on ultrasound in genetic disorders and what is the specific disorder it indicates?

Answer 10

Rocker bottom feet = Trisomy 18
Micrognathia = cri-du-chat
Anencephaly = Neural tube defect
Nasal bone hypoplasia = Down Syndrome
Enlarged nuchal translucency = Chromosomal aneuploidy

Question 11

When is chorionic villus sampling done?

Answer 11

11-12 weeks

Question 12

What genetic test is done in chorionic villus sampling?

Answer 12

FISH

Question 13

When is amniocentesis done?

Answer 13

15-18 weeks

Question 14

When can percutaneous umbilical blood sampling be done?

Answer 14

18 weeks

Question 15

What are the week marks for first, second, and third trimester?

Answer 15

1) week 1-12
2) week 13-26
3) week 27-40

Question 16

How many weeks in a full term pregnancy?

Answer 16

37-42 weeks (“normal” = 40)

Question 17

How is HbSS determined in an infant? CF? PKU? SCID?

Answer 17

HbSS = hemoglobin electrophoresis
CF = immunoreactive trypsinogen (IRT)
PKU = tandem MS
SCID = PCR for TRECs

Question 18

What are TRECs?

Answer 18

T cell receptor excision circles