Which condition is characterized by urine turning black upon standing and degenerative arthritis of the spine, hip, and knee?

The condition characterized by urine turning black upon standing and degenerative arthritis of the spine, hip, and knee is alkaptonuria. This metabolic disorder arises from a deficiency in the enzyme homogentisate oxidase, which is part of the pathway for the metabolism of the amino acids phenylalanine and tyrosine. As a result, homogentisic acid accumulates in the body and is excreted in the urine. When the urine is exposed to air, the homogentisic acid oxidizes, leading to the characteristic black discoloration.

In addition to the urinary changes, patients with alkaptonuria often develop ochronosis, which is the deposition of ochronotic pigment in connective tissues and can lead to degenerative arthritis, particularly affecting the spine, hips, and knees. This progressive joint degeneration is due to the buildup of pigment within the cartilage, causing it to become brittle and worn over time.

The other conditions listed do not present with these specific findings. Maple Syrup Urine Disease is associated with a sweet-smelling urine due to the accumulation of branched-chain amino acids. Homocystinuria typically involves intellectual disability, lens dislocation, and a risk of thromboembolism and does not cause black