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 Branched-Chain Amino Acids 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 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 Inheritance of Single-Gene Disorders 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 made of a very long strand... read more . In homocystinuria, both parents of the affected child carry a copy of the abnormal gene. Because usually two copies of the abnormal gene are necessary for the disorder to occur, usually neither parent has the disorder. (See also Overview of Hereditary Metabolic Disorders Overview of Hereditary Metabolic Disorders Hereditary metabolic disorders are inherited genetic conditions that cause metabolism problems. Heredity is the passing of genes from one generation to the next. Children inherit their parents'... read more .)
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 . 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 , and many other serious problems.
Diagnosis of Homocystinuria
Newborn screening test
Since 2008, nearly every state in the United States has required that all newborns be screened Newborn Screening Tests Many serious disorders that are not apparent at birth can nonetheless be detected by various screening tests. Early diagnosis and prompt treatment can reduce or prevent many disorders that may... read more 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 ( pyridoxine Vitamin B6 Deficiency Vitamin B6 is in most foods, but people can have vitamin B6 deficiency if they do not absorb it properly. Many foods contain vitamin B6, but extensive processing can remove the vitamin. People... read more ). Some children need to follow a special diet that restricts certain substances in protein.
Doctors may give supplements of betaine, which can help lower the levels of homocystine in the blood, and folic acid.
Children who have other forms of homocystinuria are given vitamin B12 ( cobalamin Vitamin B12 Deficiency Vitamin B12 deficiency can occur in vegans who do not take supplements or as a result of an absorption disorder. Anemia develops, causing paleness, weakness, fatigue, and, if severe, shortness... read more ) and folic acid.
The following are some English-language resources that 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.