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Screening & Prevention >> Newborn Screening >> Amino Acid Disorders >> Homocystinuria

Homocystinuria

Disorder Category

an amino acid (urea cycle) disorder

Screening

Finding

elevated methionine

Tested By

tandem mass spectrometry (MS/MS); sensitivity=NA; specificity=NA

Names

Homocystinuria

Homocystinemia

Cystathionine beta-synthase deficiency (CBS)

ICD-9

270.4, Disturbance of sulphur-bearing amino-acid metabolism

Overview

A deficiency of cystathionine beta-synthase (CBS) results in the inability to degrade homocystine to cystathionine, resulting in increased levels of homocysteine and methionine. A variant that represents a minority of cases is responsive to vitamin B6 (pyridoxine), but this type may not be detected by newborn screening.

Prevalence

about 1/200,000 - 1/300,000 live births [Homocystinuria info for professionals, STAR-G]; as high as 1:65,000 in Ireland [Homocystinuria, GeneTests.org]

Inheritance

autosomal recessive

Prenatal Testing

DNA testing by amniocentesis, or CVS; enzyme assay by amniocentesis.

Clinical Characteristics

With treatment normal IQ is possible and reduction of thromboembolic events may decrease the incidence of other sequelae, such as ectopia lentis, seizures, and psychiatric problems. Without treatment, symptoms vary widely and may present at different ages, ranging from multiple organ disease in infancy to those in early to middle adult years presenting with thromboembolism.

Initial symptoms in infants and toddlers may include:
  • developmental delay;
  • emotional and behavior problems;
  • thromboembolism; and
  • ectopia lentis (dislocation of the ocular lens) or severe myopia (nearsightedness).


Findings in older children and adults may include:
  • Marfanoid habitus: tall/ thin build; long fingers, arms, and legs;
  • genu valgum, pes cavus;
  • osteoporosis;
  • malar flush;
  • decreased hair, skin, iris pigmentation;
  • seizures;
  • vascular disease and stroke;
  • psychiatric abnormalities; and
  • mental retardation.

Follow-up on positive screening test

Quantitative plasma amino acid analysis, plasma total homocysteine analysis.

Primary care management

Upon notification of the + screen

If the diagnosis is confirmed

  • Educate the family regarding signs, symptoms, and the need for urgent care when the infant becomes ill (see Homocystinuria info for parents, STAR-G);
  • Assist in implementation and maintenance of a diet low in methionine (found in many protein-containing foods);
  • Provision of vitamin B6, betaine, vitamin B12, and folic acid may be indicated;
  • Regular blood and urine tests to monitor amino acid levels and diet may be indicated;
  • For those identified after irreversible consequences, assist in management, particularly with developmental and educational interventions.

Specialty Care Management

Initial consultation and ongoing collaboration if the child is affected. A dietician may work with the family to devise an optimal approach to dietary management.

Resources

Links

For Professionals

Homocystinuria info for professionals, STAR-G
On the Screening, Technology and Research in Genetics (STAR-G) site, one of a series of Disorder Fact Sheets for Professionals; structured list of information about the condition, with links to more information.

ACT Sheet for Homocystinuria from ACMG (pdf 118kb)
Developed by the American College of Medical Genetics (ACMG), includes recommended responses to positive newborn screening test results, diagnostic evaluation, clinical expectations, and sources of additional information. See the ACMG ACT Sheets and Confirmatory Algorithms (link elsewhere on this page) for more info and sheets on other conditions.

ACMG ACT Sheets and Confirmatory Algorithms
The American College of Medical Genetics (ACMG) has developed ACTion (ACT) Sheets and algorithms for responding to positive newborn screening test results. This page contains a table with links to all of the ACT Sheets and related algorithms.

Homocystinuria, GeneTests.org
Excellent review by Jonathan D. Picker, MBChB, PhD and Harvey L. Levy, MD including clinical description, differential, management, genetic counseling, molecular genetics, and a bibliography

Homocystinuria, OMIM
Extensive review of the literature, including clinical features and gene therapy, from the Online Mendelian Inheritance in Man site, hosted by Johns Hopkins University, providing technical information for providers on genetic disorders, links to MEDLINE, and links to other scientific information and sites.

Utah Newborn Screening Program
The site provides information and statistics about the program and related legislation, training for practices, and the conditions screened for.

For Parents

Homocystinuria info for parents, STAR-G
From the Screening, Technology and Research in Genetics (STAR-G) site, providing information for parents about homocystinuria and links to other sites including parent support groups.

Homocystinuria, Genetics Home Reference
Excellent, detailed review aimed at patients and families from the National Library of Medicine's Genetics Home Reference site.

National Urea Cycle Disorders Foundation
The National Urea Cycle Disorders Foundation, a non-profit organization, provides support services and information for families; medical lectures on urea cycle disorders; nutrition and medication resources; and information about events and conferences.

Services

Newborn Screening Programs

Utah Newborn Screening Program, more info...
44 Mario Capecchi Drive
Salt Lake City, UT84114
Phone: 801-584-8256
Fax: 801-536-0966
http://health.utah.gov/newbornscreening

Pediatric Genetics

Metabolic Clinic, more info...
100 Mario Capecchi Drive
Salt Lake City, UT84113
Phone: 801-585-2457
Fax: 585-7252
http://www.ped.med.utah.edu/divisions/divisions.htm

See all Pediatric Genetics services providers (3) in our database.

For other services related to this condition, browse our Services categories or search our database.

Helpful Articles

PubMed search for articles on homocystinuria in the last 5 years.

Authors

Reviewing Author: Nicola Longo MD, PhD, 3/2007
Compiled and edited by: Alfred Romeo RN, PhD, 3/2007
Content Last Updated: 3/2008
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