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Final Review GC > Cram 1 > Flashcards

Cram 1 Flashcards

1
Q

Which repeat disorders expand more frequently in oogenesis?

A

myotonic dystrophy (esp. congenital MD alleles (>1000))
fragile x
Friedrich’s

ataxia SCA8 (unlike other SCAs)

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2
Q

F , R, and how to calculate them

A

• F = coeffi ci ent of inbreeding - relates to a child of a consanguineous mating,
probability that the child is homozygous for a gene derived from a common
ancestor; i .e. chance to be identi cal by decent. When identical by decent –
“autozygous” • R = coefficient of r’ship – proportion of genes shared by
individuals who are relatives • If common ancestor is a carrier of a recessi ve
di sease (and we cangeneral l y assume that each person carries one autosomal
recessive disease), then the chance for a child of a consanguineous r’ship to have

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3
Q

how do you calculate F ? what is it for sibs? first cousins?

A

proportion of genes shared divided by 2. sibs share 1/2 genes, therefore F=1/4
first cousins share (1/21/21/2=1/8) their genes, therefore F=1/16

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4
Q

The coefficient of inbreeding (F ) for a mating of first cousins once removed i s: (A)

1/4 (B) l /8 (C) l /16 (D) l /32 (E) l /64

A

R - 1/16 F = 1/32

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5
Q

Assume of 100,000 consecutive newborns al l were examined for signs of an
autosomal dominant disorder with 100% penetrance. Of eight affected infants,
five were born to unaffected parents. The new mutation rate i s:

A

new mutation rate = # of affected infants born to unaffected parents divided by
total number of al l el es. 5/(2x100,000) = 2.5 x 10^5 number of sporadic cases/

total number of alleles ascertained.

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6
Q

gen pop risk for: NTD CHD cleft lip/palate

A

NTD: 1-2/1000 (caucasian) CHD: 1/100 cleftlip/pal ate: overal l : 2-4%

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7
Q

over the course of the pregnancy, what is the pattern for each of these serum

markers: hCG estri ol AFP i nhi bi nPAPP-A

A

hCG - rises rapidly early on, peaks at 10 weeks, then decline
estriol - increases with gestational age
inhibin- rise during first trimester, decline after 10th week,
stable 15th-20th week
AFP - increases and peaks at 32 weeks PAPP-A - increases

with gestation

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8
Q

initially elevated AFP is repeated i f…

A

value i s <3.0 MOM gestational age is <18weeks

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9
Q

PAPP-A where made? pattern over gestation? what patternass’d with tri 13? 18?

21?

A

made in embryo and placenta increases over gestation low level s ass’d with

13,18,21 detectable as early as 8 weeks

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10
Q

hCG where made? pattern over gestation? what pattern ass’d with tri 13? 18? 21?

other findings?

A

made by placenta rise rapidly early on and then decline between 10th and 20th
week higher levels ass’d with tri 21 (H i nit!) lower evel s ass’d with tri 18, SLOS

higher ass’d with triploidy, turner with hydrops

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11
Q

AFP where made? pattern over gestation? what pattern ass’d with tri 13? 18? 21?

other findings?

A

made by fetal liver not measurable in maternal serum until end of first trimester
rise steadily through second trimester high - NTD, abdominal wall defect l ow -

tri 21, tri 17, SLOS

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12
Q

Inhibin A where made? pattern over gestation? associations?

A

made by ovaries and fetal placenta rise during first trimester, decline after 10th
week, stable 15th-20th week twice as high in tri 21 pregnancies (has H i nit,
H=high i tri 21) high (but not l ow) level s have been associated with pregnancy

complications

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13
Q

uE3 where made? pattern over gestation? associations?

A

made by fetal adrenal glands, fetal liver, placenta rise througout pregnancy lower
in tri 21, 18 very l ow i nSLOS, antl ey-bi xl er, steroid sulfatase deficiency (x-linked
ichthyosis) only stable for 10 days, so if older sample than that will have no

detectable uE3

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14
Q

Hypoglycemia is commonly associated with the presence of abundant ketones i n
the urine. Which one of the following causes of hypoketotic hypoglycemi a (l ow
blood glucose with low urine ketones) i s the MOST common?

A

(B) Fatty acid oxidation defects

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15
Q

does tyrisone mi a type 1 have MR?

A

no

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16
Q

what is the I1307K variant?

A

in APC 6% of Ashkenazi Jews susceptibility allele, 2-3x risk not used clinically

b/c of low PPV, NPV

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17
Q

Which condition other thanHNPCC can have MSI ?

A

Turcot! FAP variant with CNS tumors, can be caused by Lynch genes

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18
Q 
When immunohistochemical (IHC) staining i s performed on a colon tumor looking
for clues about Lynch syndrome, loss of staining for which gene is most likely to

be representative of somatic mutation?

A

Somatic mutations in MLH1 are more likely due to mutations in the BRAF gene.
When BRAF is mutated, it leads to hypermethylation in MLH1, which explains

why its not seen in IHC.

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19
Q

What is hereditary colon cancer syndrome x?

A

meets Amsterdam criteria for lynch but normal MSI and IHC.

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20
Q

What are the Amsterdam and Amsterdam II criteria?

A

Amsertdam (dx’c criteria for research i n1990): 3 or more family members, 1 FDR of
the other 2, w confirmed dx of CRC** 2 successive affected generations 1 or more
CRC** dx’d <50yo -sensitivity 61% and specificity 67% for identifying MSH2 and
MLH1 mtn

AmsterdamII (modi fi ed b/c ori gi nal too stri ct): 3 or more family
members, 1 FDR to other 2, w HNPCC-related cancers** 2 successive generations
1 or more with HNPCC-related** ca <50yo -sensitivity 78%**, but lower
specificity -incorporation of MSI status or molecular diagnosis is necessary for

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21
Q

Homozygous PMS2 phenotype?

A

high risk of developing col onCA at very earl y ages (<2nd decade), as well as brain
tumors and other malignancies. al so hematologic cancer, cafe-au-l ait macules

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22
Q

what genes are associated with Turcot syndrome?

A

2/3 APC 1/3 mismatch repair genes

23
Q

Sickle cell - phenotype, lab findings for: MCV MCH Hgb (amount of Hb) Hb

electrophoresis and for trait/het?

A

HbSS - hemolytic anemia, aplastic crises, delayed growth, ischemia - acute pain,
organ damage, first manifestation is dactylitis
Hb SS
MCV: nl or increased
MCH:nl
Hgb: moderatel y decreased (anemi a)

Hb:
HbA2 <3.5%
HbS 80-90%
HbF 2-20%

S-trait
MCV: nl
MCH: nl
Hgb: nl

Hb: 
HbA 60% (reduced) 
HbS 34-42% 
HbF <1%
HbA2 1-2%
24
Q

Sickle cell /Hb C disease - phenotype? l ab findings for: MCV MCH Hgb (amount

of Hb) Hb eletrophoresis and for trait/het?

A

Hb SC - milder thanHb SS disease, but can be as severe MCV: nl MCH; nl Hgb:
mod decreased (anemi a) Hb: HbA2 <3.5% HbS 45-55% HbC 45-55% HbF 1-8%
C-trait: MCV: nl MCH: nl Hgb: nl Hb: HbA 50-60% (reduced) HbC 40-50% HbF

1%

25
Q

Beta-thal major - brief pheno l abs: MCV MCH Hgb (amount of Hb) Hb
eletrophoresis Beta-thal mi nor (hets) MCV MCH Hgb (amount of Hb) Hb

eletrophoresis

A

beta-thal maj or – microcystic hypochromic hemolytc anemia, pal l or, growth
retardation, skeletal changes, hepatosplenomegaly, etc. MCV: 50-70 (decreased)
MCH: 12-20 (decreased) Hgb (amount of Hb): <7 (decreased) Hb eletrophoresis
beta-thal-0: HbF 95-98% HbA2 2-5% HbA 0 beta-thal-+: HbF 70-90% HbA2 2-
5% HbA 10-30% beta-thal-mi nor/hets: MCV <79 (reduced) MCH <27 (reduced)
Hgb (amount of Hb) 14-15 Hb el etrophoresis HbA 92-95% (reduced) HbF 0.5-
4% (sometimes increased) HbA2 >3.5%** (increased) indicative of beta-mi nor/het

26
Q

Normal Hb studies: MCV MCH Hgb (amount of Hb) Hb el etrophoresis

A 
MCV 89.1 (mal e), 87.6 (female) 
MCH 30 Hgb 
Hb: 15.9 (mal e) 14(female) 
HbA 96%-98% 
HbF <1% 
HbA2 2%-3%
27
Q

alpha thall ab values for -mi nor (two -) -silent (one -) MCV MCH Hgb (amount of

Hb) Hb eletrophoresis

A

al pha-thal minor (2 -)
MCV: 68-84 (l ow)
MCH: 21-24 (l ow)
Hgb (amount of Hb): sl i ghtl y l ow (mi nor anemi a)

Hb el etrophoresis 
**normal ! (vs. beta-thal) 
HbA 96-98% 
HbF <1% 
HbA2 <3.5% 
alphathal si l ent (one -) 
MCV slightly decreased
MCH slightly decreased 
Hgb (amount of Hb) slightly decreased Hb
el etrophoresis *** normal (vs. beta that) 
HbA 96-98% HbF <1% HbA2 <3.5%s
28
Q

overall strategy for identifying thalassemi a carriers by CBC?

A

CBC to check for reduced MCV (alpha and beta), reduced MCH (alpha and beta),
reduced Hgb (i .e. anemi a) (al pha and beta) thenHb eletrophoresis to identify Hb
speci es: -i f normal – coul d be alpha thal -i f abnormal – which species
determine what disease -for beta thal carriers, HbA2 is increased >3.5%, HbA is

decreased

29
Q

Lab values for Hb barts and HbH disease in alpha thalassemia?

A 
Hb Barts (fatal , di ffi use edema, hepatosplenomegaly in fetus): 
MCV: >130 (very high) 
MCH: 23-40 (normal ?) 
Hgb: 3-8 (very l ow) 
Hb: Hb Bart only (no F , A, etc.) 
HbH (microcystic hypochromic hemolytic anemia, splenomegaly, mild jaundice,
skeletal changes): 
MCV 57 (ki ds), 61 (adults) (l ow) 
MCH 16-20 (l ow) 
Hgb: 8-12 (l ow) 
Hb: 
HbA 60-90% 
HbF <1% 
HbA2 <2% 
Hb Bart 2-5% 
HbH 1-40%
30
Q

what proportion(%) of spontaneous abortions result from aneupoidy?

A

50% (online course)

31
Q

what is another name for 47,XYY?

A

jacob’s syndrome

32
Q

what proportion of conceptions are aneuploid?

A

10-30% (Genzyme)

33
Q

What proportion of newborns are aneuploid?

A

0.3% (1/333)

34
Q

Prenatally, which trisomies are most common?

A

16 (31% of prenatal trisomies) 22 (10%) 21 (9%) 15 (8%) 18 (6%) 13 (5%) (genzyme)

35
Q

Age-related risks? Tri 21 and al l chromosome abnormalities?

A

tri 21 al l 33 0.16 0.29 (tri 21 ~1/2) 35 0.26 0.49 38 0.57 0.97 40 0.94 1.50 (tri 21

~2/3) 42 1.56 2.56 45 3.33 5.26 (genzyme)

36
Q

how often does confned placental mosaicism occur with CVS? what outcomes i s
it associated with? how often is it true fetal mosaicism?

A

1-2% rate of confined placental mosaicism increased risk of IUGR or IUFD
risk of UPD

10% of CPM is true fetal mosaicism (more likely if in cultured prep (type II)
and if chromosome is one of the common trisomies)

37
Q

when seen as CPM on CVS, which chromosomes are more often due to meiotic
nondisjunction and may be associated with UPD?

A

9, 16, 22

38
Q

when seen as CPM onCVS, which chromosomes are more often due to mitotic
nondisjunction and are less likely to be associated with UPD?

A

2, 7, 8, 10, 12

39
Q

which ultrasound findings have a high risk of anueploidy and what are the risks?

A 
cystic hygroma - 60% 
holoprosencephaly - 47% 
VSD - 38% 
T-E fistula - 40%
hydrops - 32% 
MCA - 29% 
CHD - 17% (Genzyme)
40
Q

what’s the empiric risk for congenital anomaly with an apparently balanced de

novo rearrangement?

A

2-3x (also: found 7x more frequently in people with MR vs. genpop’nneonates)

(Genzyme)

41
Q

how do you assess risk of anabnormal i vebornfroma carri er of a balanced

reciprocal translocati n?

A

if there’s a family history of someone with the unbalanced form then risk is highest
- 20-25%
Risk is lower if no liveborns with unbalanced and couple has had multi pl e SABs - 2-4%
If incidentally ascertained (ex. amnio for age) - 2-5%
chromosome effect - i s the unbalanced portion known to be tolerable (13, 18, 21,
8, 9 4p, 5p 18p)? then risk i s higher. (Genzyme)

42
Q

What is alternate segregation of a reciprocal translocation? what are the

outcomes? how common is it?

A

results in balanced and normal . no unbalanced outcome. most common segregation

pattern.

43
Q

what is adjacent 1 segregation of a reciprocal transolcation? what are the

outcomes? how common is it?

A

results in unbalanced. centromeres segregate as expected. i .e. homologous

centromeres separate.

44
Q

what is adjacent 2 segregation of a reciprocal translocation? what are the

outcomes? how common is it?

A

results in unbalanced. most abnormal of the 2:2 segregation patterns. homologous
centromeres segregate to the same pol e/daughter cel l . the resulting fertilized
egg has three copies of one chromosome (2 normal and one derivative) and is

monosomic for the other chromosome. rare.

45
Q

what are the risks of UPD in carriers of balanced a) homologous b) nonhomologous
robertsonian translocations? What about f the individual is phenotypically
abnormal ? When should you test a balanced robertsonian translocaiton carrier for

UPD?

A

Risk of UPD in balanced carriers 0.4-0.6% with non-homologous rob 66-73% with homologous rob

Presence of UPD in phenotypically abnormal pts 4.7% with non-
homologous rob 100% with homologous rob test for UPD if it’s 14 or 15 i neither a carrier fetus or a patient with abnormal phenotype.

46
Q

what is the empiric risk of an unbalanced karyotype in offspring of carriers of -a
pericentric in version with small distal segments? -a paracentric inversion?

A

pericentric inversion with small distal segments; 10-15% risk of unbalanced
off spring. paracentric inversion have 0.5% risk. (Genzyme)

47
Q

what are the recurring terminal deletions?

A 
del(1)(p36.3) - monosomy 1p (1/10,000)
 del(4)(p16) - Wol f-Hirschhorn(1/50,000)
del(5)(p15) - cri-du-chat (1/50,000) 
del(16)(p13.3) - Rubi nstei n-Taybi
(1/125,000) 
del(17)(p13.3) - Mi l l er-Di eker
48
Q

what conditions are seen in association with 22q11.2?

A

22q11.2 deletion synd.
dup 22q11.2 - MR, autism
4x22q11.2 - cat-eye syndrome

(usually dicentric bisatellited marker chromosome)

49
Q

which chromosome are 1/2 of all supernumary chromosomes from?

A

15 – test for UPD (in both familial and de novo cases)

50
Q

what is the most common mechanism that creates missense mutations?

A

deamination. especially a 5-methyl cytosine –> thymine

51
Q

heritability estimate from twin studies?

A

twice the difference in concordance rates between monozygotic and dizygotic
twns. ex. monozygotic concordance = 0.40 dizygotic concordance = 0.25

heritability = 0.30 (online review course)

52
Q

during the 15-20wk window of second trimester serum screening, what are each of
the analytes doing? i .e. stable, decreasing, increasing?

A

inhibinA - stable hCG - decreasing uE3 - increasing AFP - increasing

53
Q

what factors affect analyte levels in MSS and how?

A

gestational age
maternal age
maternal weight (bigger, lower medians)
race: black
(higher AFP medians); Asian and Hispanic (higher uE3 medians)
number of fetuses
diabetic status - AFP lower if insulin-dependent smoking - affects inhibin and hCG

54
Q

what is the AFP cut-off?

A

2.5MoM - for NTD, ab’l wall defect

Final Review GC (7 decks)

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