Purines (adenine, guanine)
- are metabolised to hypoxanthine
- changed by xanthine oxidase to xanthine
- Further metabolised to uric acid
Pyrimidines (thymine, cytosine)
- are metabolised to ammonium salts + urea.
Nucleoside = Base + ribose: Eg. RNA
Nucleotide = Base + ribose + phosphate radical
Classification of hyperuricaemia
- Primary: absolute/relative abnormality of xanthine-hypoxanthine handling
- Deficiency of PPRT (Lesch-Nyhan syndrome) leads to inability of xanthine/hypoxanthine to be recycled into purines
- Secondary: increased purine breakdown with increased formation of uric acid
- Ingestion - caviar, roe
- Increased cell turnover: psoriasis, sickle cell, leukaemia, malignancy
- Decreased excretion: CRF, diuretics
Complications of gout
- Joints: destructive osteoarthropathy
- Renal tract - stones, renal failure from a big stone