Homocystinuria—Amino Acid Metabolism Disorders

Metabolism is the process your body uses to make energy from the food you eat. Food is made up of proteins, carbohydrates, and fats. Your digestive system breaks the food parts down into sugars and acids, your body’s fuel. Your body can use this fuel right away, or it can store the energy in your body. If you have a metabolic disorder, something goes wrong with this process.

One group of these disorders is amino acid metabolism disorders. They include phenylketonuria (PKU) and maple syrup urine disease. Amino acids are “building blocks” that join together to form proteins. If you have one of these disorders, your body may have trouble breaking down certain amino acids. Or there may be a problem getting the amino acids into your cells. These problems cause a buildup of harmful substances in your body. That can lead to serious, sometimes life-threatening, health problems.

These disorders are usually inherited. A baby who is born with one may not have any symptoms right away. Because the disorders can be so serious, early diagnosis and treatment are critical. Newborn babies get screened for many of them, using blood tests.

Treatments may include special diets, medicines, and supplements. Some babies may also need additional treatments if there are complications.

Homocystinuria is an inherited disorder in which the body is unable to process certain building blocks of proteins (amino acids) properly. There are multiple forms of homocystinuria, which are distinguished by their signs and symptoms and genetic cause. The most common form of homocystinuria is characterized by nearsightedness (myopia), dislocation of the lens at the front of the eye, an increased risk of abnormal blood clotting, and brittle bones that are prone to fracture (osteoporosis) or other skeletal abnormalities. Some affected individuals also have developmental delay and learning problems.Less common forms of homocystinuria can cause intellectual disability, failure to grow and gain weight at the expected rate (failure to thrive), seizures, problems with movement, and a blood disorder called megaloblastic anemia. Megaloblastic anemia occurs when a person has a low number of red blood cells (anemia), and the remaining red blood cells are larger than normal (megaloblastic).The signs and symptoms of homocystinuria typically develop within the first year of life, although some mildly affected people may not develop features until later in childhood or adulthood.