The renal clearance of
cystine,
lysine,
ornithine,
arginine, and
glycine has been compared with the simultaneously determined glomerular filtration rate in nine cystinuric patients. Five were studied before and after stabilization on
penicillamine therapy, two were studied only while taking
penicillamine, and two were studied only in the absence of
penicillamine administration. The renal clearances of
cysteine-
penicillamine and of
penicillamine disulfide were also determined in the patients who were taking the
drug.
Amino acids were determined by quantitative ion exchange chromatography, and the reliability of the method has been evaluated in terms of its reproducibility and of the recovery of known amounts of
amino acids added to plasma and to urine. The plasma levels of
cystine and of the
basic amino acids were less than normal in all the patients.
Cysteine-
penicillamine and
penicillamine disulfide were cleared by the kidney at rates similar to that of
cystine. Two of the patients had
glycine clearances that were considerably above the normal value. The renal clearance of
cystine exceeded the glomerular filtration rate in six of the nine patients. The results form a continuum from values approximately equal to the glomerular filtration rate to values about twice this amount. The renal clearances of
cystine and of the
basic amino acids vary independently of one another in the disease. The significance of these results is discussed in terms of the nature of the renal tubular transport defect that underlies the disorder.