This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
All of the following are excreted in cystinuria, except: 
Select and explain. 
A. Cystine, B. Leucine, C. Arginine, D. Ornithine
B: Leucine
Answer: B: Leucine 
Explanation: Ans. b. LeucineRef: Harpers 30th Ed, Page No- 302Cystine, lysine, arginine, and ornithine are excreted in cystine-lysinuria (cystinuria), a defect in renal reabsorption of these amino acids.Apart from cystine calculi, cystinuria is benign. The mixed disulfide of 1-cysteine and 1-homocysteine excreted by cystinuric patients is more soluble than cystine and reduces formation of cystine calculi.Several metabolic defects result in vitamin B6-responsive or vitamin B6-unresponsive homocystinurias. These include a deficiency in the reaction catalyzed by cystathionine b-synthase;Serine+homocysteine-cystathionine +H2 O