Which one of the following enzymes is mainly responsible for breaking starch down into sugars?
Correct Answer A:
Amylase: breaks starch down to sugars.
Amylase is present in saliva and pancreatic secretions. It breaks starch down into sugar.
The following brush border enzymes are involved in the breakdown of carbohydrates:
Each one of the following promotes the release of endothelin, except:
Endothelin: Endothelin is a potent, long-acting vasoconstrictor and bronchoconstrictor. It is secreted initially as a prohormone by the vascular endothelium and later converted to ET-1 by the action of endothelin converting enzyme. It acts via interaction with a G-protein linked to phospholipase C leading to calcium release. Endothelin is thought to be important in the pathogenesis of many diseases including primary pulmonary hypertension (endothelin antagonists are now used), cardiac failure, hepatorenal syndrome and Raynaud's.
Promotes release:
Inhibits release:
Raised levels in:
Which one of the following diseases would give a positive cyanide-nitroprusside test?
Correct Answer C:
The cyanide-nitroprusside test would also be positive in homocystinuria.
Cystinuria is an autosomal recessive disorder characterized by the formation of recurrent renal stones. It is due to a defect in the membrane transport of cystine, ornithine, lysine, arginine (mnemonic = COLA).
Genetics:
Features:
Diagnosis:
Management:
A 23-year-old man is referred to the ophthalmologists with visual problems which are found to be caused by a downward dislocation of the lens in his right eye. The ophthalmologist notices his marfarnoid habitus and history of learning disabilities. A diagnosis of homocystinuria is suspected.
What is the pathophysiology of this condition?
Correct Answer D:
Interestingly, patients with Down's syndrome have an excess of cystathionine beta synthase.
Homocystinuria:
Homocystinuria is a rare autosomal recessive disease caused by deficiency of cystathionine beta synthase. This results in an accumulation of homocysteine which is then oxidized to homocystine.
Diagnosis is made by the cyanide-nitroprusside test, which is also positive in cystinuria.
Treatment is vitamin B6 (pyridoxine) supplements.
A new drug which may reduce the chance of patients with chronic kidney disease developing gout is introduced. In one study of 2,000 patients 1,200 received the new drug of which 120 patients develop gout. The remaining 800 patients received a placebo of which 200 developed gout.
What is the absolute risk reduction of developing gout?
Correct Answer B:
Absolute risk reduction = (Control event rate) - (Experimental event rate)
Absolute risk reduction = (Experimental event rate) - (Control event rate)
Control event rate = 200 / 800 = 0.25
Experimental event rate = 120 / 1,200 = 0.1
Absolute risk reduction = 0.25 - 0.1 = 0.15 = 15% reduction
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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