A 23-year-old female with Down's syndrome is reviewed in clinic.
Which one of the following features is least associated with her condition?
Correct Answer A: As this patient is female she is likely to be subfertile rather than infertile.
Down syndrome: features:
Clinical features:
Cardiac complications:
Later complications:
How many protein-coding genes does a haploid human genome contain?
Correct Answer B: Human genome - 25,000 protein-coding genes.
Human genome: The human genome is stored on 23 chromosome pairs. The haploid human genome has a total of 3 billion DNA base pairs, making up an estimated 20,000-25,000 protein-coding genes.
Which of the following conditions is inherited in an autosomal dominant fashion?
Correct Answer C: Autosomal recessive conditions are 'metabolic' - exceptions: inherited ataxias Autosomal dominant conditions are 'structural' - exceptions: hyperlipidaemia type II, hypokalaemic periodic paralysis.
Autosomal dominant conditions: Autosomal recessive conditions are often thought to be 'metabolic' as opposed to autosomal dominant conditions being 'structural', notable exceptions:
The following conditions are autosomal dominant:
*type 3 von Willebrand's disease (most severe form) is inherited as an autosomal recessive trait. Around 80% of patients have type 1 disease.
A 72-year-old woman is admitted for investigation of hyponatraemia.
Which one of the following features is most consistent with the syndrome of inappropriate ADH secretion?
Correct Answer E:
Hyponatraemia: Hyponatraemia may be caused by water excess or sodium depletion. Causes of pseudohyponatraemia include hyperlipidaemia (increase in serum volume) or a taking blood from a drip arm. Urinary sodium and osmolarity levels aid making a diagnosis.
Urinary sodium > 20 mmol/l:
Sodium depletion, renal loss (patient often hypovolaemic):
Patient often euvolaemic:
Urinary sodium < 20 mmol/l: Sodium depletion, extra-renal loss:
Water excess (patient often hypervolaemic and oedematous):
A study looks at the benefits of adding a new antiplatelet drug to aspirin following a myocardial infarction. The following results are obtained:
What is the number needed to treat to prevent one patient having a further myocardial infarction within 3 months?
Correct Answer E: NNT = 1 / Absolute Risk Reduction
NNT = 1 / (control event rate - experimental event rate) = 1 / (0.04-0.03) = 1 / (0.01) = 100
Numbers needed to treat and absolute risk reduction: Numbers needed to treat (NNT) is a measure that indicates how many patients would require an intervention to reduce the expected number of outcomes by one It is calculated by 1/(Absolute risk reduction) and is rounded to the next highest whole number.
Experimental event rate (EER) = (Number who had particular outcome with the intervention) / (Total number who had the intervention)
Control event rate (CER) = (Number who had particular outcome with the control/ (Total number who had the control)
Absolute risk reduction = CER-EER or EER-CER?
The absolute risk reduction (ARR) may be calculated by finding the absolute difference between the control event rate (CER) and the experimental event rate (EER). You will often find both versions of the above listed in different sources. In some ways in doesn't matter which you use as you will end up with the same answer but from a technical point of view:
*this may be more accurately termed absolute benefit increase, rather than absolute risk reduction
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