Main Campus: Chesterfield, MO 63017 | 
Homocystinuria
Cystathionine beta-synthase deficiency; CBS deficiency; HCY
Homocystinuria is an inherited disorder that affects the metabolism of the amino acid methionine. Amino acids are the building blocks of life.
Metabolism
Metabolism refers to all the physical and chemical processes in the body that convert or use energy, such as:BreathingCirculating bloodControlling bo...
Amino acid
Amino acids are organic compounds that combine to form proteins. Amino acids and proteins are the building blocks of life. When proteins are digeste...
Causes
Homocystinuria is inherited in families as an autosomal recessive trait. This means that the child must inherit a non-working copy of the gene from each parent to be seriously affected.
Autosomal recessive
Autosomal recessive is one of several ways that a trait, disorder, or disease can be passed down through families. An autosomal recessive disorder me...
Homocystinuria has several features in common with Marfan syndrome , including joint and eye changes.
Marfan syndrome
Marfan syndrome is a disorder of connective tissue. This is the tissue that strengthens the body's structures. Disorders of connective tissue affect...
Symptoms
Newborn infants appear healthy. Early symptoms, if present, are not obvious.
Symptoms may occur as mildly delayed development or failure to thrive . Increasing visual problems may lead to diagnosis of this condition.
Failure to thrive
Failure to thrive refers to children whose current weight or rate of weight gain is much lower than that of other children of similar age and gender....
Visual problems
There are many types of eye problems and vision disturbances, such as: HalosBlurred vision (the loss of sharpness of vision and the inability to see ...
Other symptoms include:
-
Chest deformities (
pectus carinatum
,
pectus excavatum
)
Pectus carinatum
Pectus carinatum is present when the chest protrudes over the sternum. It is often described as giving the person a bird-like appearance.
ImageRead Article Now Book Mark ArticlePectus excavatum
Pectus excavatum is a medical term that describes an abnormal formation of the rib cage that gives the chest a caved-in or sunken appearance....
ImageRead Article Now Book Mark Article - Flush across the cheeks
-
High arches of the feet
High arches of the feet
High arch is an arch that is raised more than normal. The arch runs from the toes to the heel on the bottom of the foot. It is also called pes cavu...
Read Article Now Book Mark Article - Intellectual disability
-
Knock knees
Knock knees
Knock knees are condition in which the knees touch, but the ankles do not touch. The legs turn inward.
Read Article Now Book Mark Article - Long limbs
- Mental disorders
- Nearsightedness
-
Spidery fingers (
arachnodactyly
)
Arachnodactyly
Arachnodactyly is a condition in which the fingers are long, slender, and curved. They look like the legs of a spider (arachnid).
Read Article Now Book Mark Article - Tall, thin build
Exams and Tests
The health care provider may notice that the child is tall and thin.
Other signs include:
-
Curved spine (
scoliosis
)
Scoliosis
Scoliosis is an abnormal curving of the spine. Your spine is your backbone. It runs straight down your back. Everyone's spine naturally curves a b...
ImageRead Article Now Book Mark Article - Deformity of the chest
- Dislocated lens of the eye
If there is poor or double vision, an eye doctor (ophthalmologist) will perform a dilated eye exam to look for dislocation of the lens or nearsightedness.
There may be a history of blood clots. Intellectual disability or mental illness is also possible.
Tests that may be ordered include any of the following:
- Amino acid screen of blood and urine
- Genetic testing
-
Liver biopsy
and
enzyme assay
Liver biopsy
A liver biopsy is a test that takes a sample of tissue from the liver for examination.
ImageRead Article Now Book Mark ArticleEnzyme assay
ELISA stands for enzyme-linked immunoassay. It is a commonly used laboratory test to detect antibodies in the blood. An antibody is a protein produ...
ImageRead Article Now Book Mark Article -
Skeletal
x-ray
x-ray
X-rays are a type of electromagnetic radiation, just like visible light. An x-ray machine sends individual x-ray particles through the body. The im...
ImageRead Article Now Book Mark Article -
Skin biopsy
with a fibroblast culture
Skin biopsy
A skin lesion biopsy is when a small amount of skin is removed so it can be examined. The skin is tested to look for skin conditions or diseases. A...
ImageRead Article Now Book Mark Article -
Standard ophthalmic exam
Standard ophthalmic exam
A standard ophthalmic exam is a series of tests done to check your vision and the health of your eyes.
ImageRead Article Now Book Mark Article
Treatment
There is no cure for homocystinuria. About half of people with the disease respond to vitamin B6 (also known as pyridoxine).
Vitamin B6
Vitamin B6 is a water-soluble vitamin. Water-soluble vitamins dissolve in water so the body cannot store them. Leftover amounts of the vitamin leav...
Those who do respond will need to take vitamin B6, B9 (folate), and B12 supplements for the rest of their lives. Those who do not respond will need to eat a low-methionine diet. Most will need to be treated with trimethylglycine (a medicine also known as betaine).
Neither a low-methionine diet nor medicine will improve existing intellectual disability. Medicine and diet should be closely supervised by a doctor who has experience treating homocystinuria.
Outlook (Prognosis)
Although no cure exists for homocystinuria, vitamin B therapy can help about half of people affected by the condition.
If the diagnosis is made in childhood, starting a low-methionine diet quickly may prevent some intellectual disability and other complications of the disease. For this reason, some states screen for homocystinuria in all newborns.
People whose blood homocysteine levels continue to rise are at increased risk for blood clots. Clots can cause serious medical problems and shorten lifespan.
Possible Complications
Most serious complications result from blood clots. These episodes can be life-threatening.
Dislocated lenses of the eyes can seriously damage vision. Lens replacement surgery may be needed.
Intellectual disability is a serious consequence of the disease. But, it can be reduced if diagnosed early.
When to Contact a Medical Professional
Call your provider if you or a family member shows symptoms of this disorder, especially if you have a family history of homocystinuria.
Prevention
Genetic counseling is recommended for people with a family history of homocystinuria who want to have children. Intrauterine diagnosis of homocystinuria is available. This involves culturing amniotic cells or chorionic villi to test for cystathionine synthase (the enzyme that is missing in homocystinuria).
If there are known gene defect in the parents or family, samples from chorionic villus sampling or amniocentesis can be used to test for these defects.
References
Rezvani I, Melvin JJ. Defects in metabolism of amino acids. In: Kliegman RM, Stanton BF, St. Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics . 20th ed. Philadelphia, PA: Elsevier; 2015:chap 85.3.
Rezvani I, Melvin JJ. Picker JD, Levy HL. Homocystinuria caused by cystathionine beta-synthase deficiency. GeneReviews. Seattle, WA: University of Washington; 2014:11. PMID: 20301697 www.ncbi.nlm.nih.gov/pubmed/20301697 .
Schiff M, Blom H. Homocystinuria and hyperhomocysteinemia. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine . 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 209.
-
Pectus excavatum - illustration
Pectus excavatum is a condition in which the "breast bone" (sternum) appears sunken and the chest concave. It is sometimes called "funnel chest". The majority of these cases are not associated with any other condition (isolated findings). However, some genetic conditions include pectus excavatum.
Pectus excavatum
illustration
-
Pectus excavatum - illustration
Pectus excavatum is a condition in which the "breast bone" (sternum) appears sunken and the chest concave. It is sometimes called "funnel chest". The majority of these cases are not associated with any other condition (isolated findings). However, some genetic conditions include pectus excavatum.
Pectus excavatum
illustration
Review Date: 10/27/2015
Reviewed By: Chad Haldeman-Englert, MD, FACMG, Fullerton Genetics Center, Asheville, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
