Cystinuria

- autosomal recessive
- defective tubular reabsorption and jejunal absorption of cysteine and dibasic amino acids (COAL - cysteine, ornithine, arginine, lysine)
- commonest cause of renal stone in children where a metabolic cause is identified
- presents with chronic backache, recurrent urinary stones
- cysteine is highly insoluble at acid pH and form radio-opaque calculi
- urine FEME: pathognomonic hexagonal crystal

- management: large fluid intake, alkalinisation of urine and penicillamine / tiopronin /captopril