Homocystinuria is a disorder of metabolism. It causes low levels of a specific enzyme. These enzymes normally help to break down the amino acids methionine and homocysteine. This causes the buildup of these amino acids.


The most common form of homocystinuria is caused by a deficiency of the enzyme cystathionine beta-synthase. Homocystinuria is a genetic disorder. Both parents must have the defective gene in order for the child to develop the condition. A number of genes have been identified such as CBS, MTHFR, MTR, MTRR, and MMADHC.

Risk Factors

Homocystinuria is more common in New South Wales, Australia, and Ireland.If both parents carry the faulty gene, there is a:
  • 25% chance the child will be born with the disorder
  • 50% chance the child will be a carrier of the faulty gene


The number and severity of symptoms vary. Symptoms may include:
  • Visual problems
  • Excessive bleeding
  • Lightheadedness
  • Flush across the cheeks, fair complexion
  • Seizures
  • Tall, thin build
  • Delays in growth
  • Long limbs
  • High-arched feet
  • Knock-knees
  • Abnormal formation of the rib cage
  • Protrusion of the chest over the sternum
  • Developmental delays
  • Learning disorders
  • Intellectual disability
Blood Clots in the Heart
Copyright © Nucleus Medical Media, Inc.
Homocystinuria may have serious complications, such as the development of blood clots. This could lead to a stroke, heart attack, or severe high blood pressure.

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