DefinitionHomocystinuria 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.
CausesThe 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 FactorsHomocystinuria 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
SymptomsThe number and severity of symptoms vary. Symptoms may include:
- Visual problems
- Excessive bleeding
- Flush across the cheeks, fair complexion
- Tall, thin build
- Delays in growth
- Long limbs
- High-arched feet
- Abnormal formation of the rib cage
- Protrusion of the chest over the sternum
- Developmental delays
- Learning disorders
- Intellectual disability
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DiagnosisEarly treatment is important. Many states require that newborns be screened for homocystinuria. The test usually looks for high levels of methionine. If the test is positive, blood or urine tests can be done to confirm the diagnosis. These tests can detect high levels of methionine, homocysteine, and other sulfur-containing amino acids. Tests to detect an enzyme deficiency may be done as well.Prenatal diagnosis of homocystinuria is available. It is done with samples taken during an amniocentesis or chorionic villi sample.To look for potential complications, the following tests may also be done:
- An eye exam
TreatmentThere is no specific cure for homocystinuria. Treatment is focused on managing the levels of methionine. It should begin as early as possible. Treatment may include medication and/or a special diet.
MedicationMany people respond to high doses of vitamin B6. The supplement will be needed for the rest of your life. A normal dose of folic acid supplement is helpful. Other medications may also be occasionally needed.
Special DietA special diet may help people who don't respond to or don't respond fully to vitamin B6 treatment. Starting the diet early in life can help prevent intellectual disability and other complications. In general, the diet:
- Restricts foods with methionine
- Consists mainly of fruits and vegetables
- Allows little, if any, meats, eggs, dairy products, breads, and pastas
PreventionGenetic counseling is advised for people with a family history of homocystinuria. The counselor will help you determine the risk your child has of developing homocystinuria.
Genetics Home Reference
National Organization for Rare Disorders, Inc.
Canadian Organization for Rare Disorders
Homocystinuria. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated September 24, 2013. Accessed May 30, 2014.
Homocystinuria. Genetics Home Reference website. Available at: http://ghr.nlm.nih.gov/condition=homocystinuria. Updated July 2011. Accessed May 30, 2014.
Homocystinuria. National Organization for Rare Disorders, Inc. website. Available at: http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/463/viewAbstract. Accessed May 30, 2014.
- Reviewer: Kari Kassir, MD
- Review Date: 02/2015
- Update Date: 05/30/2014
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