Homocystinuria

Homocystinuria (HCY)
An Amino Acid Disorder

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What is it?
Homocystinuria (HCY) is a hereditary error of metabolism. It is usually caused by a defective enzyme (cystathionine synthetase) needed to properly digest a component of food called methionine (an amino acid).

Inheritance and Frequency
Homocystinuria is thought to be inherited as an autosomal recessive genetic trait, which means the gene defect is unknowingly passed down from generation to generation. This faulty gene usually emerges when two carriers have children together and pass it to their offspring. For each pregnancy of two such carriers, there is a 25% chance that the child will be born with the disease and a 50% chance the child will be a carrier for the gene defect.

Studies conducted since 1979 show that 1 of every 200,000 live births in the United States will have Homocystinuria. Prevalence in Great Britain, Ireland, and Australia is approximately is 1 in 82,000 live births.

Signs & Symptoms
Symptoms associated with Homocystinuria may include mental retardation, seizures, psychiatric disturbances, delays in reaching developmental milestones (e.g., crawling, walking, sitting), displacement of the lens of the eye (ectopia lentis), abnormal thinning and weakness of the bones (osteoporosis and scoliosis ), and/or the formation of blood clots (thrombi) in various veins and arteries that may lead to life-threatening complications.

Long Term Effects
Optic lens dislocation may occur even with early treatment. Approximately 50% of untreated individuals die before age 25.

Treatment
Homocystinuria is treated initially by changing the baby to a formula that does not contain methionine. Treatment may also include a methionine-restricted and cystine-supplemented diet, as well as large doses of Vitamin B6.

History

Screening
Visit the What Does Your State Screen page to learn about your state's newborn screening program.

Supplemental Screening
If you live in a state that does not perform screening on its newborns for all detectable disorders, there are laboratories that will provide this screening for you no matter the state of your residence. For more information about supplemental screening, visit our supplemental screening page. Also visit our frequently asked questions page for more information on newborn screening.

Other Sites of Reference

Support Groups

National Coalition for PKU & Allied Disorders
P.O. Box 1244
Mansfield, MA 02048
Contact Person: Trish Mullaley
Phone: (877) 996-2723

Feeding Children with Special Needs

LowProtein.com Website

MUMS - National Parent-to-Parent Network

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Revised 11/22/2006