Clinical sciences Flashcards
What are funnel plots used for?
Used to demonstrate publication bias in meta analysases
How do you interpret funnel plots?
Symmetrical, inverted funnel shape - pub bias unlikely
asymmetrical funnel - relationship present between treatment effect and study size –> publication bias or systematic difference between smaller and larger studies (small study effects)
thin acending loop of henle - what can and cant get through?
Impermeable to water
Highly permeable to Na and Cl
early-onset breast cancer, sarcoma and leukaemia
Condition? gene?
Li-Fraumeni syndrome - p53 mutation
What is p53 gene for?
Crucial role in cell cycle - prevents entery into S phase until DNA has been checked and repaired
May also regulate apoptosis
Which pneumocytes secrete surfactant?
Pneumocyte type 2 - can differentiate into type 1 during lung damage
Difference between cranial and nephrogenic DI
Cranial - deficiency of ADH
Nephrogenic - insensitivity to ADH
Where does ADH act and what does it do?
ADH promotes water reabsorption via insertion of aquaporin 2 channels in collect ducts
What triggers release of ADH?
extracellular fluid osmolality increase
volume decrease
pressure decrease
angiotensin II
What reduces secretion of ADH?
extracellular fluid osmolality decrease
volume increase
temperature decrease
C1 inhibitor (C1-INH) protein deficiency - consequence?
causes hereditary angioedema
C1-INH is a multifunctional serine protease inhibitor
probable mechanism is uncontrolled release of bradykinin resulting in oedema of tissues
C1q, C1rs, C2, C4 deficiency (classical pathway components) - consequence?
predisposes to immune complex disease
e.g. SLE, Henoch-Schonlein Purpura
C3 deficiency - consequence?
causes recurrent bacterial infections
C5 deficiency - consequence?
predisposes to Leiner disease
recurrent diarrhoea, wasting and seborrhoeic dermatitis
C5-9 deficiency - consequence?
encodes the membrane attack complex (MAC)
particularly prone to Neisseria meningitidis infection
What diseases is endothelin involved in?
primary pulmonary hypertension (endothelin antagonists are now used),
cardiac failure,
hepatorenal syndrome
and Raynaud’s.
Calculation of absolute risk reduction?
Absolute risk reduction = (Control event rate) - (Experimental event rate)
Where in nephron does majority of glucose reabsorption occur?
Proximal convoluted tubule
What is the genetic phenomenon of anticipation? Which disorders are more likley to experience this?
earlier onset in successive generations
Particularly present in trinucleotide repeat disorders
Most common cause of Down Syndrome (genetically)
Nondisjunction
prenatal tests showing low circulating levels of pregnancy-associated plasma protein-A (PAPP-A) and an abnormal nuchal translucency screening test
Diagnosis?
Downs syndrome
Examples of mitochondrially inherited disease?
Leber’s optic atrophy
symptoms typically develop at around the age of 30 years
central scotoma → loss of colour vision → rapid onset of significant visual impairment
MELAS syndrome: mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes
MERRF syndrome: myoclonus epilepsy with ragged-red fibres
Kearns-Sayre syndrome: onset in patients < 20 years old, external ophthalmoplegia, retinitis pigmentosa. Ptosis may be seen
sensorineural hearing loss
Children of fathers with mitochondrialy inherited disease?
For a man with mitochondrial disease, none of his children will inherit the condition
What is Gaucher’s disease? How does it present?
Gaucher’s disease is an autosomal recessive disease and it is the most common lipid storage disorder
Leads to accumulation of glucocerebrosidase in brain, liver and spleen
Present with hepatosplenomegaly and aseptic necrosis of femur
Which metabolic disorder causes:
Developmental delay
Cherry red spot on macula
+- hepatosplenomegaly
If no hepatosplenomegaly - Tay-Sachs disease
If hepatospenomegaly - Niemann-Pick disease
Most common cardiac and renal abnormalities in Turner’s?
Cardiac - Biscuspid aortic valve (15%), coarctation of aorta (5-10%)
Increased risk of aortic dilatation and dissection
Renal - horseshoe kidney
What does specificity and sensitivity mean?
Specificity - Proportion of patients without the condition who have a negative test result
TN / (TN + FP)
Sensitivity - Proportion of patients with the condition who have a positive test result
Sensitivity = TP / (TP + FN )
What is lead time bias?
Occurs when two tests for a disease are compared, the new test diagnoses the disease earlier, but there is no effect on the outcome of the disease
HLA DR3 is associated with which conditions?
dermatitis herpetiformis
Sjogren’s syndrome
primary biliary cirrhosis
T1DM (More strongly associated with DR4)
How to calculate NTT?
NNT = 1 / Absolute Risk Reduction
Short stature + primary amenorrhoea
Diagnosis?
Turners syndrome
What are the parametric tests and non-parametric tests? When to use which?
Parametric - normally distributed data
Parametric tests:
- Students t test (paired v unpaired - single group of patients if paired)
- Pearsons product moment coefficient - correlated
Non-parametric tests
- Mann Whitney U test
- Wilcoxon signed rank test
- Chi-squared test
- Spearman, Kendall rank - correlation
Which statistical test to use when:
comparing ordinal, interval, or ratio scales of unpaired data
Mann-Whitney U
Nominal = categorical = qualitative
No sense of order
E.g ; sex , color
Frequency/proportion ; percentages
Ordinal
Rank , satisfaction , fanciness
Frequency/proportion ; percentages
Interval / ratio = scale = quantitative = parametric
Number of costumers
Weight
Age
Size
Which statistical test to use when:
comparing two sets of observations on a single sample, e.g. a ‘before’ and ‘after’ test on the same population following an intervention
Wilcoxon signed rank
Which statistical test to use when:
Comparing proportions or percentages e.g. compares the percentage of patients who improved following two different interventions
Chi-squared
Karyotype in Turners?
45 XO
Which dermatological condition is associated with Coeliac - how does this look? Which HLA is this associated with?
Dermatitis herpetiformis - intensely itchy, papulovesicular, blistering rash, similar to that seen in herpes infection
Associated with HLA DR3
How can you work out variance if you know SD?
SD^2 = variance
Which studies are most affected by recall bias?
Case control studies
Multiple sarcomas at young age - what genetic condition and what gene + its role?
Li-Fraumeni syndrome
Mutation in p53 (tumour suppressor gene 17p) - holds cell cycle at G1/S phase checkpoint allowing for detection + repair of DNA damage
When is the mean, mode and median the same?
in a normal distribution of data-
Which chromosome encodes for HLA antigens?
Chromosome 6
Why can sepsis lead to Hypotension?
Sepsis -> release of IL1 which causes vasodilation and hence hypotension
What do the different subunits of troponin bind to?
troponin C: binds to calcium ions
troponin T: binds to tropomyosin, forming a troponin-tropomyosin complex
troponin I: binds to actin to hold the troponin-tropomyosin complex in place
What is the purpose of secondary messenger system? what can trigger the cGMP system?
Secondary messengers - allow for amplification of external stimulus
ANP and NO act as ligand hormones for cGMP system
What describes the power of a study? how can you calculate it?
the probability that a statistically significant difference will be detected / probability of (correctly) rejecting the null hypothesis when it is false / which also means the probability of confirming the alternative hypothesis when the alternative hypothesis is true
Power = 1 - probability of type 2 error (beta)
Inheritance of G6PD?
X linked recessive so no male to male transmission
Hence titos son’s can’t have G6PD
Where is phosphate reabsorbed in the nephron?
PCT is responsible for phosphate reabsorption
What are the main parts of antibodies and what binds to each part?
Fab region: antigen-binding fragment - the region that binds to antigens
Fc region: fragment crystallizable region - the tail region of an antibody that interacts with cell surface receptors
Reactive arthritis HLA?
HLA B27
What is Fabry disease? How is it inherited?
X linked recessive - lysosomal storage condition
leads to kidney failure, HF, body pain and skin issues
What is a type 2 error in stats?
Type II error - the null hypothesis is accepted when it is false
What is the usual outcome measure in cohort studies?
Relative risk
What cytokine is involved in development of granulomas?
Inf-gamma = used in macrophage activation which leads to the formation of granuloma
may be useful in chronic granulomatous disease and osteopetrosis
What happens during reverse transcriptase PCR? what is this used for?
RNA is converted to DNA
It is used to detect gene expression
the probability of obtaining a result by chance at least as extreme as the one that was actually observed, assuming that the null hypothesis is true
What does this describe?
P value
how can you calculate standard error of mean?
Standard deviation / square root (No. of patients)
Difference between type 1 and 2 errors?
Type I: the null hypothesis is rejected when it is true (false +ve)
Type II: the null hypothesis is accepted when it is false (false -ve)
What are some examples of X linked dominant conditions?D
Alports
Retts
Vit D resistant rickets
What is the main action of PCR reactions?
DNA amplification
What is incidence?
The incidence is the number of new cases per population in a given time period.
What is prevalence? point v period?
The prevalence is the total number of cases per population at a particular point in time
point prevalence = number of cases in a defined population / number of people in a defined population at the same time
period prevalence = number of identified cases during a specified period of time / total number of people in that population
What is the relationship between incidence and prevalence?
prevalence = incidence * duration of condition
in chronic diseases the prevalence is much greater than the incidence
in acute diseases the prevalence and incidence are similar. For conditions such as the common cold the incidence may be greater than the prevalence
Early strokes / MIs + proteinuria + typical rash (angiokeratomas)? How does the rash look and what is the condition / inheritances?
rash in a bathing-suit distribution - angiokeratomas
X linked recessive deficiency of alpha-galactosidase A -> FABRY DISEASE
When to use Wilcoxon signed rank test?
Non-parametric
compares two sets of observations on a single sample, e.g. a ‘before’ and ‘after’ test on the same population following an intervention
Effect of metanalyses on power and p value v individual studies?
Increase power
decreaase p value
Which virus is a RF for oropharnyngeal ca? what else is this a RF for?
HPV 16/18
Also for cervical, vulval, anal, penile
Which Ca is increased risk with EBV?
Burkitt’s lymphoma
Hodgkin’s lymphoma
Post transplant lymphoma
Nasopharyngeal carcinoma
Risk of which ca with Hep B+C?
HCC
Human T-lymphotropic virus 1 increased risk of which conditions?
Adult T cell leukaemia
Tropical spastic paraparesis
How to calculate NNT? and everything in the calculation?
1/(Absolute risk reduction)
Absolute risk reduction = CER-EER or EER-CER
EER = (Number who had particular outcome with the intervention) / (Total number who had the intervention)
CER = (Number who had a particular outcome with the control/ (Total number who had the control)
Homocystinuria - what is the tx?
B6 (Pyridoxine) supplementation
What are the features of diabetic nephropathy under biopsy?
Kimmelstiel-Wilson lesions (odulular hyaline areas develop in the glomuli), nodular glomerulosclerosis
What are diseases inherited in a mitochondrial pattern? (5)
Leber’s optic atrophy
symptoms typically develop at around the age of 30 years
central scotoma → loss of colour vision → rapid onset of significant visual impairment
MELAS syndrome: mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes
MERRF syndrome: myoclonus epilepsy with ragged-red fibres
Kearns-Sayre syndrome: onset in patients < 20 years old, external ophthalmoplegia, retinitis pigmentosa. Ptosis may be seen
sensorineural hearing loss
ABL is the oncogene for?
Chronic myeloid leukaemia
c-MYC and n-MYC is the oncogene for?
cMYC = Burkitt’s lymphoma
nMYC = Neuroblastoma
BCL2 is the oncogene for?
Follicular lymphoma
RET is the oncogene for?
Multiple endocrine neoplasia (types II and III)
RAS is the oncogene for?
Many cancers especially pancreatic
erb-B2 is the oncogene for?
erb-B2 (HER2/neu) = Breast + ovarian Ca