Cram 2

Question 1

what are the risk cutoffs (in CA) for T21, T18, SLOS i nMSS?

Answer 1

T21 - 1/150 T18 - 1/100 SLOS - 1/250

Question 2

ethnicity-based screening in prenatal clinic (based onLuanne Hudgins’ lecture)

Answer 2

al l women: screen for thalassemi as -MCV -i f MCV <80 - hemogl obi n
el ectrophoresi s Afri can-ameri can: si ckl e cel l -hemogl obi nel ectrophoresi s northern
european: CF -25 most commonmutati ons AJ: -tay-sachs serumscreeni ng -canavan,
CF , fami l i al dysautonomi a by mol ecul ar testi ng -uponrequest - expanded panel -
fancC, ni eman-pi ck type A, bl oom, MPS 4, Gaucher 1 french canadi an: -tay-sachs
serumscreeni ng SMA - controversi al (ACMG endorses, ACOG doesn’t)

Question 3

what is the false positive rate of PGD?

Answer 3

5-10% amnio or CVS recommended

Question 4

what is one situation that PUBs is useful for?

Answer 4

u/s shows fetus has bilateral absence of radii fetus may have thrombocytopenia
absent radii (TAR). PUBS allows for study of fetal platelets.

Question 5

how is spina bifida diagnosed by ultrasound?

Answer 5

not by detecting the lesion itse f. by detecting the associated secondary findings
in the fetal skull - ‘lemon sign” and ‘banana sign.’ dx can be made by u/s 80% of

the ti me.

Question 6

which disorder is better tested by CVS than amnio?

Answer 6

OI - b/c collagen studies need to be done onCVS sample.

Question 7

what fraction of trisomy 16 onCVS is CPM?

Answer 7

all of it, essentially. so no risk for even mosaic trisomy 16. but, there are
assocaited negati ve outcomes: increased risk preeclampsia and IUGR

Question 8

what is the most common risk from2nd trimester amniocentesis?

Answer 8

rupture of fetal membranes. will often seal over. this i s more common than

miscarriage.

Question 9

what is the recurrence risk for spina bifida when a couple had a previous child

with spina bifida?

Answer 9

2-3% (vs. 0.1% genpop)

Question 10

is there an association between maternal age and AFP levels?

Answer 10

no!! AFP and the things it tests for are independent of maternal age and so AFP
doesn’t need to be adjusted based on maternal age.

Question 11

NTD risk factors?

Answer 11

maternal valproic acid exposure i n1st tri mester (1% ri sk) spina bifida in parent (2-
3% risk) race (NTD more common among whites and Hispanics) folic acid
deficiency maternal obesity maternal increased body temperature in 1st trimester

Question 12

what should you do if a pregnant woman has a big NT >3.0 (? >4.0)?

Answer 12

no need to do serumscreen, b/c chance of chromosomal abnormal ity i s so hi gh.
offer 1) CVS, 2) fetal echo, 3) targeted u/s at 18 weeks

Question 13

what is an increased nuchal translucency associated with?

Answer 13

trisomy 21, 18, 13 turner syndrome cardi ac abnormalities noonan syndrome skeletal
dysplasias congenital diaphragmatic hernia many other rare genetic conditions

Question 14

which trisomy is better picked up by first trimester screening than by second

trimester screening?

Answer 14

trisomy 13 - b/c many have an increased NT

Question 15

a sequence is?

Answer 15

single event, usuaslly of unknown etiology, that leads to multiple deformations

and disruptions

Question 16

what is the notable feature of aicardi syndrome?

Answer 16

retinal lacunae

Question 17

what are the empiric and theoretical risks for a first cousin mating to have a child

with birth defects, genetic disorder, etc?

Answer 17

theoretical : R=1/8, F=1/16, chance of rare AR disease =1/32 = ~3% empiric risk

for birth defects (T&T) = 3.6%

Question 18

what is the limit of consanguinity in terms of genetic significance?

Answer 18

consanguinity among individuals that are 3rd cousins or more distantly related is

not genetically significant.

Question 19

how does recombination distance (θ) compare to physical distance (base pairs)?

Answer 19

θ = 0.01 = 1cM ~ 1 Mb (1x10^6 bp) (average gene i s 10-15kb or 0.015 Mb)

Question 20

how do you calculate new mutation rate given an incidence and fitness?

Answer 20

The new mutation rate (u) i s equal to the al l el e frequency * selection(s); and s = 1
– fitness (f) ex. incidence = 1/45,000 fitness = 0.1 q = (1/2)(1/45,000) = 1/90,000

s = 0.9 u = (0.9) (1/90,000) = 1/100,000

Question 21

bayes, HW, other mat

Answer 21

read the question!! what are they asking for?! after you’re done, re-read the
question. did you answer what they are asking for?