What causes cystine crystal in the urine?

Cystine crystals in the urine are primarily caused by a genetic disorder known as cystinuria, which affects the kidneys' ability to reabsorb cystine, an amino acid. This leads to elevated levels of cystine in the urine, where it can precipitate and form crystals. Factors such as dehydration and urinary pH can also influence the formation of cystine crystals. Individuals with cystinuria are at an increased risk for kidney stone formation due to these crystals.