Which of the following conditions is not caused by a trinucleotide repeat expansion?
Correct Answer C:
Trinucleotide repeat disorders:
Trinucleotide repeat disorders are genetic conditions caused by an abnormal number of repeats (expansions) of a repetitive sequence of three nucleotides. These expansions are unstable and may enlarge which may lead to an earlier age of onset in successive generations - a phenomenon known as anticipation*. In most cases, an increase in the severity of symptoms is also noted.
Examples - note dominance of neurological disorders:
*Friedreich's ataxia is unusual in not demonstrating anticipation
Each one of the following causes of hyponatraemia is associated with a urinary sodium of less than 20 mmol/L, except:
Correct Answer E:
Syndrome of inappropriate ADH is associated with urinary sodium > 20 mmol/l.
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:
1- Sodium depletion, renal loss (patient often hypovolaemic):
2- Patient often euvolaemic:
Urinary sodium < 20 mmol/l:
1- Sodium depletion, extra-renal loss:
2- Water excess (patient often hypervolaemic and oedematous):
A study is designed to assess the efficacy of a new anti-hypertensive medication. Two groups of patients are randomly assigned, one to take the established drug for 3 months whilst the other takes the new drug for 3 months. Blood pressure is measured before and after the intervention. There is then a period off medication for 1 month. After this period has elapsed the medication that the groups receive is swapped around and again blood pressure is measured before and 3 months later. The difference in blood pressure after the respective medications is calculated for each patient.
Which one of the following significance tests is it most appropriate to apply?
Correct Answer B:
This describes a crossover study. As we are comparing parametric data from the same patients (they swapped medication halfway through the study) the Student's paired t-test should be used.
Significance tests: types:
The type of significance test used depends on whether the data is parametric (something which can be measured, usually normally distributed) or non-parametric.
Parametric tests:
Non-parametric tests:
Paired data:
Which one of the following is the most common genetic cause of Prader-Willi syndrome?
Correct Answer A:
Deletion of chromosome 15:
1- Prader-Willi syndrome Prader-Willi syndrome is an example of genetic imprinting where the phenotype depends on whether the deletion occurs on a gene inherited from the mother or father:
2- Prader-Willi syndrome is associated with the absence of the active Prader-Willi gene on the long arm of chromosome 15. This may be due to:
Features:
A middle-aged man is diagnosed with nasopharyngeal carcinoma.
What type of virus family is associated with this malignancy?
The Epstein-Barr virus is one of the herpes viruses.
Epstein-Barr virus: associated conditions:
Malignancies associated with EBV infection:
The non-malignant condition hairy leukoplakia is also associated with EBV infection.
*EBV is currently thought to be associated with both African and sporadic Burkitt's.
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