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Medical Genetics Review Course > Molecular > Flashcards

Molecular Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

4 benifits of MLPA for Duchenne Muscular Dystrophy testing

A
  • Specific allele detection
  • Copy number detection (deletion/duplication)
  • Methylation status
  • Carrier screening
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2
Q

Percentage risk for gonadal mosaicism in Duchenne Muscular Dystrophy

A

Risk of gonadal mosaism is 15%

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3
Q

Risk of germline mosaisism and recurrance risk in after a woman who has an afected child, is not found to have a DMD variant

A

Risk of gonadal mosaism X chance of transmitting

15% X 1/2 = 7% Recurrance risk

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4
Q

The majority of cases of achondroplasia are caused by this variant

A
  • FGFR3*
    p. Gly380Arg

99% G>A transistion

1% G>C transversion

80% de novo (paternal)

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5
Q

Juvanille repeats in Huntington Disease >60 repeats: an increase of > 7 repeats in the next generation is usually inherited from which parent

A

Paternal

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6
Q

WHat is the benifit of using linked markers to determine an at risk grandchild for Huntington’s disease

A

Linked markers look at “at risk” alleles and this does not change the parental risk with an at risk grandchild.

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7
Q

What is the smallest number of repeats that have been documented to expand in a Fragile X carrier?

A

56 CGG repeats

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8
Q

What number of repeats in a Fragile X carrier is amost 100% likly to expand in the next generation

A

100 CGG repeats

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9
Q

Modality used to identify Fragile X carriers and those affected

A

Triple primed PCR with methylation (extra step)

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10
Q

What is the signifigance of the poly T tract in CF mutation carriers

A

The poly T tract in intron 8 results in skipping of exon 9

resulting in a dysfuctional CFTR transcript or no transcript

the 5T allele results in 90% of transcripts without exon 9

p.Phe508del is a LD with the 9T Allele

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11
Q

What are the limitation of Sanger Sequencing

A

Can only analyze one sample at a time

cannot detect large deletions and duplications

not good for large repeat expansions

Allelic dropout

missed low level mosaicism

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12
Q

Most individuals who are RhD negative have a complete ______ of the gene

A

Deletion

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13
Q

Why is the mother sample needed for genetic testing for hemolytic Disease of the newborn

A

No maternal sample–> hard to interprate

could represent a true Rh positive fetus

could also represent Rh neg fetus with intact D gene or at least some portion of the D gene

Therefore the maternal sample is needed

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14
Q

Chromosomal microarrays are limited and cannot detect

A

Balanced translocations

Inversions

Polyploidy

UPD with fully parental heterodisomy

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15
Q

What is the benifits of using SNP genotyping with CGH array

A

Can be used to detect

  • Consangunity
  • Uniparental Disomy
  • Long continuous stretches of homozygosity (>5Mb)
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16
Q

What are the 4 possible genetypes detected by SNP array in a sample that shows a duplication?

A
  1. BBBB
  2. BBBA
  3. AAAB
  4. AAAA
17
Q

What is the Log2Ratio found for a duplication on aCGH

A

+0.6

18
Q

ACMG recommends array based technology as the first tier for?

A
  1. Developmental delay and/or cognitive impairment DD/DI)
  2. Autism Spectrum Disorder (ASD/PDD)
  3. Multiple congenital anomalies
  4. Epilepsy
19
Q

What are advantages of using microarray vs karyotype to analyze products of conception

A

CMA adds 10% sensitivity for miscariages

Finds pathogenic microdeletions and duplications

No need for culture–> faster TAT

20
Q

In general, microscopically visable CNVs > ____ are reportable

A

>3-5Mb

21
Q

Uncle-neice union

coefficient of consanguinity ((F)

A

1/4

22
Q

Uncle-neice union coefficient of inbreeding

A

1/8

23
Q

First cousins

coefficient of consanguinity (F)

A

1/8

24
Q

First cousins coeeficient of inbreeding

A

1/16

25
Q

First cousins once removed coefficient of consanguinity (F)

A

1/16

26
Q

First cousins once removed

coefficient of inbreeding

A

1/32

27
Q

What type of responders to codeine may get the drug to fast leading to respiratory distress

A

Ultrarapid-responders

CYP2D6

Codeine–>active form of morphine

N.Africans, Ethiopians, Saudi Arabians (16-28%)

28
Q

CYPC19 poor responders to this medication cannot prevent clots, may need to take another drug

A

Clopidogrel (Plavix)

29
Q

Poor metabolizers to Warfarin with these two mutations may be at risk for bleeding

A
  • CYP2C9*
  • VKORC1*

poor metabolizer- need to reduce dose

ultrarapid metabolizer- need to increase dose

30
Q

Specific amino acid substitions in these genes may interfere with binding of this drug to kinase

used to treat CML and GIST (KIT mutations)

A

Imatinib Mesylate

CYP3A4 and CYP3A5

T3151I

31
Q

HLA-B*5701 variants and Abacavir may put patient at increase risk for life threatening condition

A

Steven-Johnson Syndrome

32
Q

The FDA recommends TPMT genotyping or phenotyping before starting this medications

A

Azathioprine

This allows patients who are at increased risk for toxicity to be identified and for the starting dose of azathioprine to be reduced, or for an alternative therapy to be used

Azathioprine is a prodrug that must first be activated to form thioguanine nucleotides (TGNs), the major active metabolites. Thiopurine S-methyltransferase (TPMT) inactivates azathioprine, leaving less parent drug available to form TGNs.

An adverse effect of azathioprine therapy is bone marrow suppression, which can occur in any patient, is dose-dependent, and may be reversed by reducing the dose of azathioprine

33
Q

About what percentage of carriers of DMD have clinically signifigant cardiomyopathy

A

about 8%

34
Q

What are the various ways a female with features of DMD can arise? (5)

A
  1. Skewed X- inactivation
  2. Turner syndrome 45, X
  3. Balanced X-autosome translocation (non-translated X is inactivated and DMD variant is on translocated active X)
  4. Uniparental disomy X
  5. Compound heterozygosity
35
Q

What is the residual risk of a mother with negative genetic analysis for DMD having second son with DMD?

A

Residual Risk of 7%

Germline mosaisim up to 10-15% in mothers with negative genetic analysis

36
Q

Acoording to the DMD practice guildines what is the first test that should be ordered if one is considering a diagnosis of DMD?

A

CPK

If not elevated DMD is not likly and should consider an alternative diagnosis

Order of evaluation

CPK–>DMD CNV analysis–>DMD sequence–>Muscle biopsy

37
Q

what are the limitations of CNV by MLPA for DMD?

A

Allelic dropout

False positives: single exon deletion due to SNV under probe–>should confirm by sequencing

Limited by the amount of probes per reaxn.

38
Q

Eteplirsen induces skipping of what exon for DMD tx.

A

exon 51

39
Q

These repeats within the CGG repeats of FMRP result in less liklihood of CGG repeating in the next generation

A

AGG repeats

Medical Genetics Review Course (11 decks)

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