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Homocystinuria

By

Matt Demczko

, MD, Sidney Kimmel Medical College of Thomas Jefferson University

Last full review/revision Apr 2020| Content last modified Apr 2020
CLICK HERE FOR THE PROFESSONAL VERSION

Homocystinuria is a disorder of amino acid metabolism Overview of Amino Acid Metabolism Disorders Amino acid metabolism disorders are hereditary metabolic disorders. Hereditary disorders occur when parents pass the defective genes that cause these disorders on to their children. In most... read more that is caused by a lack of the enzyme cystathionine beta-synthase, which is needed to metabolize homocysteine. This disorder can cause a number of symptoms, including decreased vision, intellectual disability, and skeletal abnormalities. Homocystinuria occurs when parents pass the defective genes Genes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells... read more Genes that cause this disorder on to their children.

  • 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 Proteins Carbohydrates, proteins, and fats supply 90% of the dry weight of the diet and 100% of its energy. All three provide energy (measured in calories), but the amount of energy in 1 gram (1/28 ounce)... read more are the building blocks of proteins and have many functions in the body. 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.

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 Osteoporosis Osteoporosis is a condition in which a decrease in the density of bones weakens the bones, making breaks (fractures) likely. Aging, estrogen deficiency, low vitamin D or calcium intake, and... read more 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 Intellectual Disability Intellectual disability is significantly below average intellectual functioning present from birth or early infancy, causing limitations in the ability to conduct normal activities of daily... read more are common. Homocystinuria makes the blood more likely to clot spontaneously, resulting in strokes Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more , high blood pressure High Blood Pressure High blood pressure (hypertension) is persistently high pressure in the arteries. Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying... read more High Blood Pressure , and many other serious problems.

Diagnosis of Homocystinuria

  • Newborn screening 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

Doctors may give supplements of betaine, which can help lower the levels of homocystine in the blood, and folic acid.

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Preventive Health Care Visits in Infants
Frequent doctor visits are recommended for all infants younger than 1 year of age. These visits, also called well-child visits, make it possible to check development, look for health problems, provide age-appropriate vaccinations, and educate parents. Which of the following is a condition that might affect some infants born very prematurely, with less than 32 weeks of development in the uterus?
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