Homocystinuria is a rare genetic disorder that affects the body's ability to process certain amino acids, particularly methionine. This condition is caused by a deficiency in the enzyme cystathionine beta-synthase, which leads to the accumulation of homocysteine in the blood and urine. Symptoms can include developmental delays, vision problems, and an increased risk of blood clots. Diagnosis typically involves blood and urine tests to measure levels of homocysteine and other related substances. Treatment often includes dietary changes, such as a low-methionine diet, and supplementation with vitamins like B6, B12, and folate to help manage symptoms and reduce complications.