Homocystinuria is a disorder of amino acid metabolism that is caused by a lack of the enzyme cystathionine beta-synthase, which is needed to metabolize the amino acid homocysteine. This disorder can cause a number of symptoms, including decreased vision, intellectual disability, and skeletal abnormalities. Homocystinuria occurs when parents pass on to their children the defective genes that cause this disorder.
Homocystinuria is caused by a lack of the enzyme needed to metabolize homocysteine.
Symptoms include intellectual disability, eye problems, and abnormalities of the skeleton.
The diagnosis is based on a blood test.
A special diet and supplements of vitamin B6, betaine, and folic acid may help some children.
Amino acids are the building blocks of proteins and have many functions in the body. The body makes some of the amino acids it needs and gets others from food.
Children with homocystinuria are unable to break down (metabolize) the amino acid homocysteine, which, along with certain toxic by-products, builds up to cause a variety of symptoms. Symptoms of homocystinuria range from mild to severe.
There are different types of inherited disorders. In homocystinuria, both parents of the affected child carry 1 copy of the abnormal gene. Because usually 2 copies of the abnormal (recessive) gene are necessary for the disorder to occur, usually neither parent has the disorder. (See also Overview of Hereditary Metabolic Disorders.)
Symptoms of Homocystinuria
Infants with this disorder are normal at birth. The first symptoms, including dislocation of the lens of the eye causing severely decreased vision, usually begin after 3 years of age.
Most children have skeletal abnormalities, including osteoporosis. Children are usually thin with a curved spine, chest deformities, elongated limbs, and long, spiderlike fingers.
Without early diagnosis and treatment, mental (psychiatric) and behavioral disorders and intellectual disability are common.
Homocystinuria makes the blood more likely to clot spontaneously, resulting in strokes, high blood pressure, and many other serious problems.
Diagnosis of Homocystinuria
Newborn screening test
In the United States, most states require that all newborns are screened for homocystinuria with a blood test.
A test measuring enzyme function in the liver and DNA tests are done to confirm the diagnosis of homocystinuria. Tests of skin cells may also be done.
Treatment of Homocystinuria
Vitamin B6 and a special diet
Some children with homocystinuria improve when given vitamin B6 (). Some children need to follow a special diet that restricts certain substances in protein.
Children who have other forms of homocystinuria are given vitamin B12 (cobalamin) and folic acid.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
National Organization for Rare Disorders (NORD): This resource provides information to parents and families about rare diseases, including a list of rare diseases, support groups, and clinical trial resources.
Genetic and Rare Diseases Information Center (GARD): This resource provides and easy to understand information about rare or genetic diseases.
