Homocystinuria

Synonyms

• None

Disorder Subdivisions

• None

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). Due to deficiency of the CBS enzyme, infants with 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). Additional skeletal abnormalities may include progressive sideways curvature of the spine (scoliosis), abnormal protrusion or depression of the breastbone (pectus carinatum or excavatum), and generalized loss of bone density (osteoporosis). In addition, in those with the disorder, blood clots may tend to develop or become lodged within certain large and small blood vessels (thromboembolisms), potentially leading to life-threatening complications.

Homocystinuria due to deficiency of cystathionine synthase is inherited as an autosomal recessive trait. The disorder results from changes (mutations) of a gene on the long arm (q) of chromosome 21 (21q22.3) that regulates the production of the CBS enzyme.

Resources

CLIMB (Children Living with Inherited Metabolic Diseases)
Climb Building
176 Nantwich Road
Crewe, Intl CW2 6BG
United Kingdom
Tel: +44 870 7700 325
Fax: +44 870 7700 327
Email: info@climb.org.uk
Internet: http://www.CLIMB.org.uk

March of Dimes Birth Defects Foundation
1275 Mamaroneck Avenue
White Plains, NY 10605
Tel: (914)428-7100
Fax: (914)997-4763
Tel: (888)663-4637
Email: Askus@marchofdimes.com
Internet: http://www.marchofdimes.com

The Arc (a national organization on mental retardation)
1010 Wayne Ave
Suite 650
Silver Spring, MD 20910
Tel: (301)565-3842
Fax: (301)565-3843
Tel: (800)433-5255
TDD: (817)277-0553
Email: info@thearc.org
Internet: http://www.thearc.org/

NIH/National Digestive Diseases Information Clearinghouse
2 Information Way
Bethesda, MD 20892-3570
Tel: (301)654-3810
Fax: (301)907-8906
Tel: (800)891-5389
Email: nddic@info.niddk.nih.gov
Internet: http://www.niddk.nih.gov

Belgian Association for Metabolic Diseases (BOKS)
Alice Nahonlann 7
Melsele, 9120
Belgium
Tel: 3237754839
Email: info@boks.be
Internet: http://www.boks.be

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc. ® (NORD). A copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see http://www.rarediseases.org/search/rdblist.html

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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.

For additional information and assistance about rare disorders, please contact the National Organization for Rare Disorders at P.O. Box 1968, Danbury, CT 06813-1968; phone (203) 744-0100; web site www.rarediseases.org or email orphan@rarediseases.org

Last Updated: 3/20/2000
Copyright 1987, 1988, 1990, 1994, 1995, 1996, 1997, 1998, 1999, 2000 National Organization for Rare Disorders, Inc.