Types of Stones
in the urine, or cystinuria, is a relatively rare autosomal recessive
inborn error of metabolism which is characterized by impaired reabsorption
of dibasic amino acids (cystine, lysine, ornithine and arginine)
from the renal tubules as well as the gastrointestinal tract. Only
the basic amino acid, cystine, is associated with stone formation
due to its poor solubility. Cystine stones represent 1 to 4% of
all urinary calculi. The prevalence in the United States is 1 in
15,000 persons. It accounts for 6 to 8% of pediatric stones. Successful
medical therapy in treatment of patients with cystine stones is
based on three factors:
Decreasing total urinary cystine concentration
2. increasing the solubility of cystine
3. Decreasing urinary cystine excretion.
medical management can be achieved by a combination of these therapeutic
measures. This includes adequate fluid hydration and fluid diuresis.
In addition, urinary alkalinization to a pH of 7.5 or higher with
potassium citrate can decrease the solubility of cystinuria. In
addition, D-penicillamine decreases the urinary excretion of cystine
by binding cystine to form the more soluble cystine - S - penicillamine
complex that is 50 times more soluble than cystine. However, numerous
side effects including rash, fever, agranulocytosis, iron depletion,
proteinuria and nephrotic syndrome have limited its use. Alpha-mercapto-propionyl-glycine,
or Thiola, a newer agent with similar action to penicillamine, has
fewer side effects.
Cystinuria, an autosomal recessive disease, results from excessive
excretion of the four basic amino acids, cystine, ornithine, lysine,
and arginine (COLA) into the urine. Cystine is relatively insoluble
in acid urine. Patients with cystinuria (>250mg/24 hr.) produce
a supersaturated urine and are at risk for crystallization and stone
formation. The chemoprevention of cystine stones includes hydration
and urinary alkalinization, cystine-binding agents (D-penicillamine,
alphamercaptopropionylglycine, captopril), and irrigation chemolytic
therapy (tromethamin E, acetylcysteine).
Fitomer WL, Pak CYC. Recent advances in the biochemical and molecular
biological basis of cystinuria. J Urol 1996, 156:6:1907-1912.
SD, Resnick MI. Cystine calculi: Diagnosis and management. Urol
Clin North Am 1997, 24:1:163-171.