Uric Acid Metabolism Flashcards
What are purines?
Ubiquitous Biomolecules
Adenosine, Guanosine and Inosine: Genetic code A and G
Second Messengers for hormone action e.g. cAMP
Energy transfer e.g. ATP
What is purine catabolism?
What is the plasma concentration of monosodium urate?
Men: 0.12 – 0.42 mmol/l
Women: 0.12 – 0.36 mmol/l
What is the solubility of monosodium urate?
37C: 0.40 mmol/l
30C: 0.27 mmol/l
pH dependent
What is Lesch Nyhan syndrome?
Complete HGPRT deficiency.
- Normal at birth
- Developmental delay apparent at 6/12
- Hyperuricaemia
- Choreiform movements (1 year)
- Spasticity, mental retardation
- Self mutilation (85%) aged 1-16
What is Gout?
Monosodium urate crystals
Can be acute (Podagra) or chronic (Tophaceous)
Males 0.5 – 3% prevalence
Females 0.1 – 0.6% prevalence
Post pubertal males and post menopausal females
What ar clinical features of acute gout?
Rapid build up of pain
“Exquisite”
Affected joint red, hot and swollen
1st MTP joint first site in 50%
This joint is involved in 90% overall
What is the treatment of acute gout?
- NSAIDs
- Colchicine
- Glucocorticoids
Do NOT attempt to modify plasma urate concentration.
What is the management of hyperuricaemia (interval (non acute) gout)?
Drink plenty (water!)
Reverse factors putting up urate
Reduce synthesis with allopurinol
Increase renal excretion with probenecid: “uricosuric”
What are the side effects of allopurinol?
Interacts with azathioprine, making it more toxic on bone marrow etc.
Azathioprine is metabolised to mercaptopurine and then to thioinosinate which interferes with purine metabolism.
Allopurinol makes the mercaptopurine last longer.
How is gout diagnosed?
Tap effusion
View under polarised light
Use red filter
What are the features of gout (uric acid crystals)?
Needle-shaped and yellow (negatively birefringent)
What is this?
Negatively birefringent crystals
What is this?
Positively birefrigent crystals
What is pseudogout?
Occurs in patients with osteoarthritis
Pyrophosphate crystals
Self limiting 1-3 weeks
