is a hereditary defect in the kidney´s ability to reabsorb cystine and the amino acids Arginine, Lysine and Ornithine from the urine. Unfortunately, cystine is poorly soluble in the urine and tends to form stones in the urinary tract if the concentration is too high. Cystine stones represent about 1-2% of urinary stones in adults. Arginine, Lysine and Ornithine, do not form stones.
The symptoms of cystinuria are the same as from other stones in the urinary tract, regardless of origin. Thus, when a stone gets trapped in the kidney or the ureter the patient suffers from intense and recurrent pain. The urine may also contain visible blood.
Cystinuria is diagnosed by measuring the concentration of cystine in the urine. This is usually done in young patients who suffers from kidney stones and in patients with kidney stones in the family.
The most usual form of cystinuria (type I, also called type A) is inherited in an autosomal recessive way. The gene involved is named SLC3A1. The cystine concentration in the urine is usually in the thousands (umol/L). If only one chromosome is affected the person has no increased concentration of cystine in the urine and no cystine stone formation.
In the less common form of cystinuria (non type I, or type B), only one chromosome needs to be affected to have an increase in cystine concentration i.e. autosomal dominant inheritance. The gene involved in this type of cystinuria is named SLC7A9. The urinary cystine concentration in the heterozygotes are usually in the high hundreds (umol/L) and may form stones. The homozygotes have the same very high urinary concentration as homozygote type I.
Treatment of cystinuria
The treatment of cystinuria is usually a triad:
However, if potassium citrate cannot be used (e.g. due to hyperkalaemia, dyspepsia etc), it is better to use sodium containing preparations (e.g. sodium bicarbonate) as compared to no alkalizing treatment.