B8-066 Genetic Counseling

Question 1

PPV is […] proportional to prevalence

Answer 1

directly

(as prevalence in a population increases, so does PPV)

Question 2

carrier screening is recommended for [4]

Answer 2

cystic fibrosis
spinal muscular atrophy
hemoglobinopathies
fragile X

(additional considerations for special populations as well)

Question 3

in fragile X, risk for expansion is based on […]

Answer 3

CGG repeats

(less than 45 normal, 50-200 increases risk, 200+ is full mutation)

Question 4

people of Ashkenazi Jewish descent should have preconception screeing for [4]

Answer 4

canavan disease
CF
familial dysautonomia
Tay-Sachs

Question 5

placenta biopsy at 10-13 weeks gestation

Answer 5

chorionic vilus sampling

Question 6

testing performed on IVF embryo

Answer 6

preimplantation genetic testing (PGT)

Question 7

extract fetal cells at 15+ weeks gestation

can also look at hormones, enzymes, and infectious causes

Answer 7

amniocentesis

Question 8

the presence of two or more populations of cells within an organism, each with a different genetic composition

Answer 8

mosaicism

Question 9

first trimester screening can be done as early as […] weeks

Answer 9

10

Question 10

what serum markers does the quad screen evaluate? [4]

Answer 10

hCG
AFP
unconjugated estriol
inhibin

Question 11

[quad screen]
elevated hCG
elevated HI (inhibin)

Answer 11

Trisomy 21

Question 12

[quad screen]
low hCG
low estriol

Answer 12

trisomy 18

Question 13

[quad screen]
isolated elevated AFP

Answer 13

neural tube defect
ventral wall defect

Question 14

big fluid collection on the back of the fetus’s neck

Answer 14

cystic hygroma

(50% risk of aneuploidy- esp. trisomy 21 and Turners)

Question 15

what are the most common conditions cfDNA is testing for? [4]

Answer 15

T21
T18
T13
sex chromosomes

(SNP methods can occasionally identify more)

Question 16

what screening test has the highest sensitivity and specificity for Trisomy 21?

Answer 16

cfDNA