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USMLE® Step 1 flashcards
1
Q

Define intention to treat analysis

A

A comparison of the treatment groups which includes all patients as originally allocated, post-randomisation. Inclusion occurs regardless of deviations occurring post-randomisation.

Preserves the prognostic balance generated by allocation

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2
Q

Calculate the QALY for someone with 2 years, with full QoL

A

2 x 1 = 2 QALYs

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3
Q

What is the DAVID software used for?

A

Shows patterns in families of genes, and the statistical probability that RNA is involved in the process

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4
Q

How would you confirm which gene is the mutant gene?

A

Another cell should be transfected

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5
Q

Outline the stages of a drug trial

A
  1. Idea 2. Basic research 3. Drug development 4. Clinical trials- phases 1-3 5. Regulatory approval 6. Patient care
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6
Q

What are the two parts of CRISPR

A

Guide RNA that recognizes specific traces of viral DNA and attaches to it The enzyme Cas9 that cuts the DNA

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7
Q

The aim of phase 1 clinical trials

A

-ensure there are no major safety issues -ensure it can reach the targeted body area -ensure it can remain long enough to deliver treatment -gain preliminary evidence that it could offer therapeutic value

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8
Q

What is the declaration of Helsinki?

A

Ethical principles for medical research involving human subjects.

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9
Q

Describe the method of PCR

A
  1. select the unique sequence and form a forwards and reverse primer with it
  2. mix primers and DNA sample
  3. Heat to 96*C and cool to 60*C
  4. Add DNA polymerase and dNTPs to synthesise new DNA strand
  5. Heat to 72*c for DNA polymerase to bind
  6. Repeat (x30)
  7. Separate DNA using electrophoresis on agarose gel
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10
Q

How would you calculate sensitivity

A

TP/(TP+FN)

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11
Q

Give 2 benefits of RCT

A
  1. Good randomization will “wash out” any population bias
  2. Easier to blind/mask than observational studies
  3. Results can be analysed with well-known statistical tools
  4. Populations of participating individuals are clearly identified
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12
Q

Definition: Gene Therapy

A

The introduction of genes into an afflicted individual for therapeutic reasons

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13
Q

Give 2 benefits of a case report

A
  1. Can help in the identification of new trends or diseases
  2. Can help detect new drug side effects and potential uses (adverse or beneficial)
  3. Educational – a way of sharing lessons learned
  4. Identifies rare manifestations of a disease
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14
Q

Describe the animal model for synthetic heroin

A
  1. MPTP given to marmozets destroying dopaminergic neurons 2. can then study effects of Parkinson’s in animals 3. several therapies consequently discovered 4. drugs/treatments then tested
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15
Q

Give 2 benefits of a systematic review

A
  1. Exhaustive review of the current literature and other sources
  2. Less costly to review prior studies than to create a new study
  3. Less time required than conducting a new study
  4. Results can be generalized and extrapolated into the general population more broadly than individual studies
  5. More reliable and accurate than individual studies
  6. Considered an evidence-based resource
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16
Q

Define Case Report

A

An article which describes and interprets an individual case

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17
Q

Define RCT

A

Randomly assigns participants to groups (intervention or control). The only expected difference should be the condition

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18
Q

If the A average cost is £2,000, and the B average cost is £3,000, and the A average QALY is 2 and the B average QALY is 4, calculate the £ per QALY gained

A

3,000/4 - 2,000/2 = 1,000/4 = £500 per QALY gained

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19
Q

True or false: SNPs are a cause of disease

A

False- they are associated with it

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20
Q

Define transgene

A

cDNA coding for any gene introduced into a cell

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21
Q

Trisomies are ….

A

conditions where there are 3 chromosomes present instead of 2

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22
Q

What is the purpose of RNA sequencing

A

Measures changes in gene expression

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23
Q

Difference Between Knockout and Transgenic

A
  • knock-out animals is to eliminate functional copies of a gene, we must specifically target the natural copy of the gene - unlike the transgenics, where insertion can be at a random location
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24
Q

What is the difference between PCR and qPCR

A

RT-PCR used to amplify RNA to cDNA. Quantitative PCR- used to measure the specific amount of target DNA (or RNA) in a sample

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25
Q

Define Pedigree of Family

A

A diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next,

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26
Q

How are imaging methods used in diagnostic tests/screens

A

• All use combinations of parameters: shape, size, number, specific molecule • Scoring systems often used, subjectivity can be an issue, expert opinion often required

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27
Q

What are the two assumptions PCR depends on?

A
  1. viral sequence <300 bp long
  2. 18-20 bp of viral DNA not found elsewhere in the human genome
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28
Q

Give 2 disadvantages of a case report

A
  1. Cases may not be generalizable
  2. Not based on systematic studies
  3. Causes or associations may have other explanations
  4. Can be seen as emphasizing the bizarre or focusing on misleading elements
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29
Q

Explain how the Wakefield MMR study contravened ethical guidelines and demonstrated a conflict of interests

A
  • ‘MMR vaccine gives you autism’
  • Falsified by several papers who disproved this
  • ‘All media lies’
  • VERY limited paper- strong conclusions drawn from weak evidence
  • The lancet then proved no correlation, but the doubt was already in the public mind
  • Wakefield was being funded through solicitors seeking evidence to use against vaccine manufacturers
  • So entirely biased/flawed from the start
  • Children were picked by Wakefield to try and support his hypothesis, but he misreported his findings i.e. some kids he said had diseases didn’t
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30
Q

What do GWAS look for?

A

Single nucleotide polymorphisms (SNPs) which are over-represented in diseased patients.

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31
Q

Give one aim of gene therapy

A

to insert a normal allele of the defective gene into the somatic cells of the tissue affected by the disorder traceable to a single defective gene

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32
Q

Define blinding

A

Patients or physicians do not know which treatment group they are assigned too- helps to prevent bias

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33
Q

What is Karl Popper’s theory of falsification

A
  1. Come up with an idea/hypothesis 2. Test it to destruction 3. You cannot prove a hypothesis is true- you can corroborate it 4. If you can prove a hypothesis is false- this is falsification.
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34
Q

Which type of study would be best for identifying potential causes of disease?

A

Prospective cohort

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35
Q

Give 2 benefits of a case-control study

A
  • Good for studying rare conditions or diseases
  • Less time needed to conduct the study because the condition or disease has already occurred
  • Lets you simultaneously look at multiple risk factors
  • Useful as initial studies to establish an association
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36
Q

Describe what is meant by a paradigm shift

A

Contradictory evidence builds up, so a new paradigm is proposed and tested.

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37
Q

Who is included in an intention to treat analyses

A

Everyone- no one is excluded

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38
Q

What are the steps in a trio analysis

A
  1. deep sequence both parents
  2. deep sequence proband
  3. observe differences- heterozygotic change
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39
Q

give 2 disadvantages of a systematic review

A
  • Very time-consuming
  • May not be easy to combine studies
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40
Q

Drugs can also be tested in vitro- but why is in vivo better?

A

in the body there are -cell to cell contacts/co-culture -3D not 2D matrix structure -complex signals e.g. hormones -matrix flexibility -normoxic conditions

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41
Q

What is GWAS

A

an approach used in genetics research to ASSOCIATE specific genetic variations (genotype) with particular diseases (or phenotype)

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42
Q

Describe trio analysis

A

Sequence the affected proband and both unaffected parents to look for de novo changes in the child.

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43
Q

Define proband

A

Affected individual

44
Q

Definition: Transgenic Animals

A

an organism whose genome contains DNA introduced from another organism of the same or a different species

45
Q

State Koch’s 4 postulates

A
  1. The germ is present in all with the disease (not healthy)
  2. Microorganisms must be isolated from a diseased organism and grown in pure culture
  3. Cultured microorganisms should cause disease in healthy tissue
  4. The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host.
46
Q

Define case-control study

A

compares patients/those with disease or outcome of interest with controls who don’t. Retrospectively looks at how frequently exposure to a risk factor is present.

47
Q

Define cohort study

A

One or more samples followed prospectively and status evaluations with respect to a disease are measured

48
Q

How does a NIPS work

A

Via next generation sequencing- e.g. counts number of reads on chr21 (compare fetal and maternal ratios)

49
Q

Give 3 disadvantages of using a disease model

A
  1. strain of mouse will affect genes
  2. different circadian rhythms
  3. scientists stress mice
  4. cage is hyper-hygienic -animals not human so not same mechanisms
50
Q

What is the cut-off value per person for an ICER to be accepted?

A

£30,000

51
Q

What are Single nucleotide polymorphisms (SNPs)

A

single base pair differences in the sequences of a particular region of DNA from one individual compared to another of the same species or population

52
Q

Define exome

A

Section of the genome coding for a protein

53
Q

How would you calculate specificity

A

TN/(FP+TN)

54
Q

Define randomisation

A

patients are assigned to groups recieving different treatments- helps to reduce bias whether intentional/unintentional

55
Q

Give 2 disadvantages of a cohort study

A
  • Cohorts can be difficult to identify due to confounding variables
  • No randomization, which means that imbalances in patient characteristics could exist
  • Blinding/masking is difficult
  • Outcome of interest could take time to occur
56
Q

Define single blind

A

usually refers to the patient being blinded but not the administering clinician

57
Q

Explain how and why the Nuremberg trials, the Tuskegee Study and the Alder Hey tissue scandal contributed to modern ethical guidelines and the Human Tissue Act

A
  • -New guidelines were introduced as a result
  • -ethics approval committees were established
  • -Huge public mistrust of the scientific community/conspiracy theories
58
Q

Give 2 disadvantages of RCT

A
  • Expensive in terms of time and money
  • Volunteer biases: the population that participates may not be representative of the whole
  • Does not reveal causation
59
Q

If blinding is not possible, what could happen instead

A

observers not involved in the patient’s care may be used

60
Q

Define True Positives

A

have the disease and correctly test positive

61
Q

What does GWAS stand for?

A

Genome wide association studies

62
Q

5’ GGCTATCCG 3’ 3’ CCGATAGGC 5’

If both strands of this DNA could be transcribed:

  1. the two strands would be transcribed from left to right
  2. the two strands would be transcribed from right to left
  3. The upper strand would be transcribed from left to right and the lower strand would be transcribed from right to left
  4. The upper strand would be transcribed from right to left and the lower strand would be transcribed from left to right
A

d) The upper strand would be transcribed from right to left and the lower strand would be transcribed from left to right

63
Q

Describe Phase 2 clinical trial

A

Only if phase 1 is successful.

Occurs in a larger group of people, and often contains patients who have the targeted condition.

Drug performance may be compared against pre-existing treatment/placebo

64
Q

Steps to Develop a Transgenic Animal

A
  1. Remove eggs and fertilize them in vitro
  2. Clone the desired gene from the donor organism
  3. Inject the cloned DNA directly into the nuclei of the fertilized eggs
  4. Some of the cells express the foreign gene
  5. Developed embryos are implanted into the surrogate mother, once born are transgenic animals
65
Q

What is a NIPS

A

Non-invasive prenatal screen (NIPS) for trisomy

66
Q

Define systematic review

A

provides a comprehensive review of all relevant studies on a clinical/health related topic question

67
Q

State the 3 NICE economic considerations

A
  1. Cost-effectiveness is determined by an analysis of the ratio of cost to health effect (QALY)
  2. Considers how many people are affected by the condition and the dehabilitation
  3. Pharma/Biotech industry must mitigate the risk of a negative recommendation of NICE
68
Q

What are volatile organic compounds (VOCs)

A

Metabolic products present in sweat, faeces, urine and breath

69
Q

Define genetic linkage

A

a measure of how resistant to recombination a genetic marker and phenotype are

70
Q

The aim of phase 3 clinical trials

A
  • demonstrate safety and effectiveness of new medicine/vaccine
  • confirm dosage levels
  • identify side-effects/contraindications
  • compare against existing treatments
71
Q

How to calculate a QALY

A

Life Expectancy x HR-QoL

72
Q

Purpose of Transgenic Animals

A

(1) make proteins in large amounts for pharmaceutical purposes (2) study gene expression (3) GMO (longer self life, bigger animals, more food)

73
Q

What are the steps of GWAS

A
    1. DNA purified from both controls and patients
  2. Polymorphisms should be individually mapped
  3. These can then then be analysed and over-representations (SNPs) spotted
74
Q

Define False positives

A

do not have the disease but incorrectly test positive

75
Q

What are the 7 declarations of Helsinki

A
  1. Societal/Scientific Value
  2. Scientific validity
  3. Fair subject selection
  4. Favourable risk-benefit ratio
  5. Respect for subjects
  6. Informed consent
  7. Independent review
76
Q

Define False negatives

A

have the disease but incorrectly test negative

77
Q

Describe the purpose of the SCID-NOD mouse

A

no immune system, so allows tissue grafting can also inject human bone marrow

78
Q

Define knock-out model

A

genes can be removed to identify their effects/physiological functions -this can test treatments + reveal developmental role

79
Q

Give 2 disadvantages of a case-control study

A
  • Problems with data quality because they rely on memory/recall
  • Not good for evaluating diagnostic tests because it’s already clear that the cases have the condition and the controls do not
  • It can be difficult to find a suitable control group
80
Q

What is a conditional knock out

A

those in which a gene is lost only in particular tissues and/or at a particular time

81
Q

Define knock-in model

A

Specific changes in a gene can be added to an organism/introduce specific mutations

82
Q

Give 2 benefits of a cohort study

A
  • Subjects in cohorts can be matched, which limits the influence of confounding variables
  • Standardization of criteria/outcome is possible
  • Easier and cheaper than a randomized controlled trial (RCT)
83
Q

what are some advantages to CRISPR

A

quicker, cheaper and more efficient

84
Q

What is cell free DNA

A

• DNA released into the blood • Tumour and normal cells • Non-invasive test

85
Q

What is combined to generate a trisomy risk score

A

nuchal translucency, [PAPP-a], [HcG] and mothers age

86
Q

Define CRISPR

A

a gene editing tool which uses the Cas 9 system

87
Q

How to calculate Incremental Cost Effectiveness Ratio (ICER)

A

Difference in costs/Difference in QALYs = Cost per QALY gained

88
Q

True or False: Pseudoscience provides falsifiable hypotheses; science does not.

A

False- Science provides falsifiable hypotheses; pseudoscience does not.

89
Q

Purpose of Knockout Animals

A

Remove both alleles of a normal gene the animal express to compare the value of the gene - done to understand the purpose of the gene and its effect on the phenotype

90
Q

Define double blind

A

Neither patient or clinician know which treatment is randomised to

91
Q

What are the steps of RNA sequencing

A
  1. RNA isolated RNA reverse
  2. transcribed into cDNA
  3. DNA sequenced
  4. Analysed as a graph to see which genes are expressed
92
Q

Why are accurate diagnostics tests important

A

• Correct therapy can be used • Early detection of diseased can give a better prognosis • We need good tests and know how to interpret them

93
Q

Give 3 benefits of using a disease model

A
  1. small/fast breeding
  2. easily edit genes
  3. can replicate human symptoms/phenotype
  4. share a similar genome
  5. mammals
  6. 3D model
94
Q

Define sequencing

A

determine the primary structure of nucleotides

95
Q

When would an amniocentesis be offered?

A

risk is >1 in 150

96
Q

Define True negatives

A

do not have the disease and correctly test negative

97
Q

If it takes 18 cycles of qPCR to detect a RAS signal in a control line, and 14 cycles in a cancerous line, how many cycles difference is there? and what does this mean?

A

4 cycles- so cancerous has more RAS signals than control

98
Q

What are some uses of PCR

A
  • Detection of viral and bacterial DNA in tissue samples.
  • Determining the size of a sequence of DNA between two ‘primers’.
  • Production of DNA for making genetic tools (e.g. expression vectors) or DNA sequencing.
99
Q

Give some uses of qPCR

A
  • Quantifying viral load.
  • Comparing amounts of DNA.
  • Comparing amounts of specific mRNA (following conversion to DNA by RT)
100
Q

Give some uses of RNA sequencing

A
  • Comparative gene expression.
  • Finding out which genes are regulated in a particular disease or in response to a specific stimulus.
  • An un-biased method.
101
Q

Give some uses of DNA sequencing

A
  • Mutation detection
  • Pathogen identification
  • Gene identification
102
Q

What are some uses of Genome sequencing

A
  • Gaining all data on genetic variation.
  • Identification of spontaneous mutations
103
Q

Give some uses of GWAS

A
  • Understanding pathways involved in complex diseases.
  • Assessment of individual’s disease risk.
104
Q

What is Trio analysis used for

A

Identification of the cause of rare genetic diseases.

105
Q

What is a use of Western Blotting

A
  • Determine changes in protein level.
  • Disease/ tissue specific expression.
106
Q

What is a genetic screen for?

A

Identification of genes important for a particular physiological or developmental process.

107
Q

What is ELISA used for

A
  • Determine changes in protein level.
  • Detection of viral protein.
  • Detection of antibody response.
  • Detection of secreted molecules eg. TNFalpha

Principles of Medical Research (3 decks)

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