Homocystinuria due to Cystathionine Beta-Synthase Deficiency

National Organization for Rare Disorders, Inc.

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Disorder Subdivisions

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General Discussion

Homocystinuria is a rare metabolic condition characterized by an excess of the compound homocystine in the urine. The condition may result from deficiency of any of several enzymes involved in the conversion of the essential amino acid methionine to another amino acid (cysteine)--or, less commonly, impaired conversion of the compound homocysteine to methionine. Enzymes are proteins that accelerate the rate of chemical reactions in the body. Certain amino acids, which are the chemical building blocks of proteins, are essential for proper growth and development.

In most cases, homocystinuria is caused by reduced activity of an enzyme known as cystathionine beta-synthase (CBS). Infants who develop homocystinuria due to CBS deficiency (which is also known as classical homocystinuria) may fail to grow and gain weight at the expected rate (failure to thrive) and have developmental delays. By approximately age three, additional, more specific symptoms and findings may become apparent. These may include partial dislocation (subluxation) of the lens of the eyes (ectopia lentis), associated "quivering" (iridodonesis) of the colored region of the eyes (iris), severe nearsightedness (myopia), and other eye (ocular) abnormalities. Although intelligence may be normal in some cases, many children may be affected by progressive mental retardation. In addition, some may develop psychiatric disturbances and/or episodes of uncontrolled electrical activity in the brain (seizures). Affected individuals also tend to be thin with unusually tall stature; long, slender fingers and toes (arachnodactyly); and elongated arms and legs ("marfanoid" features). In addition, affected individuals may be at risk for the development of blood clots that can become lodged within certain large and small blood vessels (thromboembolisms), potentially leading to life-threatening complications. Homocystinuria due to deficiency of CBS deficiency is inherited as an autosomal recessive trait. The disorder is caused by changes (mutations) of a gene on the long arm (q) of chromosome 21 (21q22.3) that regulates the production of the CBS enzyme.

Supporting Organizations

Belgian Association for Metabolic Diseases

Floralaan 35A
Beveren, 9120
Belgium
Tel: 03 775 48 39
Fax: 03 775 48 39
Email: info@boks.be
Website: http://www.boks.be/site/index.php/

CLIMB (Children Living with Inherited Metabolic Diseases)

Climb Building
176 Nantwich Road
Crewe, CW2 6BG
United Kingdom
Tel: 4408452412173
Fax: 4408452412174
Email: enquiries@climb.org.uk
Website: http://www.CLIMB.org.uk

Genetic and Rare Diseases (GARD) Information Center

PO Box 8126
Gaithersburg, MD 20898-8126
Tel: (301)251-4925
Fax: (301)251-4911
Tel: (888)205-2311
Website: http://rarediseases.info.nih.gov/GARD/

HCU Network Australia

9 Stone Cottage Court
Castle Hill, NSW 2154,
Australia
Website: http://www.hcunetworkaustralia.org.au/

March of Dimes

1275 Mamaroneck Avenue
White Plains, NY 10605
Tel: (914)997-4488
Fax: (914)997-4763
Email: AskUs@marchofdimes.org or preguntas@nacersano.org
Website: http://www.marchofdimes.org and nacersano.org

NIH/National Institute of Neurological Disorders and Stroke

P.O. Box 5801
Bethesda, MD 20824
Tel: (301)496-5751
Fax: (301)402-2186
Tel: (800)352-9424
Website: http://www.ninds.nih.gov/

Save Babies Through Screening Foundation

P.O. Box 42197
Cincinnati, OH 45242
USA
Tel: (610)251-9876
Fax: (610)647-5757
Tel: (888)454-3383
Email: email@savebabies.org
Website: http://www.savebabies.org

The Arc

1825 K Street NW, Suite 1200
Washington, DC 20006
Tel: (202)534-3700
Fax: (202)534-3731
Tel: (800)433-5255
Email: info@thearc.org
Website: http://www.thearc.org

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders (NORD). For a full-text version of this report, go to www.rarediseases.org and click on Rare Disease Database under "Rare Disease Information".

The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only.

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This disease entry is based upon medical information available through the date at the end of the topic. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.

Last Updated:  4/27/2015
Copyright  2015 National Organization for Rare Disorders, Inc.