What human disease is characterized by the absence of a carrier protein that transports cysteine?

Cystinuria is characterized by a defect in the renal tubular reabsorption of certain amino acids, specifically cysteine, ornithine, lysine, and arginine. The underlying mechanism involves a mutation in the genes responsible for encoding the sodium-dependent neutral amino acid transporters in the kidneys. This defect results in the inability to effectively transport cysteine back into the bloodstream from the urine, leading to elevated levels of cysteine in the urine.

The accumulation of cysteine can lead to the formation of kidney stones, which can cause significant pain and complications if not managed appropriately. Recognizing cystinuria is essential for implementing preventive strategies to reduce the risk of stone formation, including increased hydration and dietary modifications.

The other options refer to different metabolic disorders not related to cysteine transport. Maple syrup urine disease arises from a deficiency in the branched-chain alpha-keto acid dehydrogenase complex, affecting the metabolism of certain amino acids. Phenylketonuria is caused by a deficiency in phenylalanine hydroxylase, leading to elevated levels of phenylalanine. Alkaptonuria occurs due to a deficiency in the enzyme homogentisate oxidase, resulting in the accumulation of homogentisic acid. These conditions