Homocystinuria is an inherited disorder that keeps the body from
processing the essential amino acid methionine. Amino acids are the building
blocks of protein. Methionine occurs naturally in various proteins. Infants
need it for growth, and adults need it to maintain their body’s
The illness usually affects infants during the first few years
of life, and the more rare forms of the disorder can lead to children being
underweight. If it’s left untreated, homocystinuria can have serious and sometimes
What Are the Signs
and Symptoms of Homocystinuria?
The symptoms will depend on the type of homocystinuria. Symptoms
generally develop during the first years of life. However, some people
experience symptoms during adulthood. Symptoms are often vague and difficult to
detect. The most common forms of this disorder may involve the following
- dislocation of the lenses in the eyes
- abnormal blood clots
- osteoporosis, or weakening of the bones
- learning disabilities
- developmental problems
- chest deformities, such as a protrusion or a caved-in
appearance of the breastbone
- long, spindly arms and legs
Less common variations involve these additional signs and
- megaloblastic anemia, an anemia involving
larger-than-normal red blood cells
- failure to thrive
- intellectual disabilities
- movement and gait abnormalities
What Are the Types
Numerous variations of homocystinuria exist. They range from
common to rare. No specific names exist for these variations. Instead, they’re
distinguished by their symptoms.
Infants who are affected by the common form of this disorder
generally experience mild symptoms. In fact, they may not even have symptoms
that require treatment until they’re older. However, the less common forms
of this disorder have been known to cause more serious developmental problems,
including impaired intellectual capability.
Certain genetic mutations present at birth cause this disease.
More than 150 mutations that cause homocystinuria have been found in the gene
cystathionine beta-synthase, which is also known as the CBS gene. The CBS gene
holds instructions for making an enzyme that uses vitamin B-6 to metabolize the
amino acids homocysteine and serine. The mutations prevent the normal
functioning of the CBS gene. This results in a buildup of homocysteine and
other toxins that damage the nervous system, which includes the brain, and the
In rare cases, mutations in other genes like MTHFR, MTR, or MTRR
cause the disorder. Homocystinuria is an autosomal recessive trait. This means
that for a child to have the signs or symptoms of this condition, they would
need to inherit the mutated gene from both parents.
Who Is at Risk for
Since homocystinuria is passed from parents to children, a
family history of the disorder places children at an increased risk of developing
this condition. The disorder is more common in:
Your child’s doctor may look for certain signs to
determine whether you or your child has this condition. An extremely thin or
tall child is more likely to have the condition. Additionally, their doctor may
search for signs such as chest deformities, a curvature of the spine, and
dislocated lenses in the eyes. An eye examination can reveal a dislocated lens
if your child experiences double or significantly impaired vision.
Your doctor may also order a series of tests to determine if
your child is affected. These tests may include:
testing to look for one of the genes involved in the disorder
amino acid screen of the blood and urine to check for excess homocysteine
test to determine the body’s
response to consuming methionine
liver biopsy and enzyme assay to check enzymatic activity
Other tests that may be done to determine
the impact of the disease include X-rays to look for signs of osteoporosis, a
skin biopsy, and a fibroblast culture.
There’s no cure for homocystinuria. High doses of vitamin B-6 are a
successful treatment for about half of
the people with this disorder. If you respond well to this supplementation, it’s
likely that you’ll have to use daily vitamin B-6 supplements for the rest of
Alternatively, if you don’t experience positive
results from this therapy, your doctor may recommend eating a diet low in foods
containing the amino acid methionine. People diagnosed at an early stage have
had positive responses after switching to this diet.
Your doctor may also recommend taking betaine (Cystadane).
Betaine is a nutrient that works to remove homocysteine from the blood. Taking
a folic acid supplement and adding the amino acid cysteine to the diet are
What Can I Expect If
My Child Has Homocystinuria?
There’s currently no cure available for this disorder. However, around
of people who are diagnosed with this condition show improvement from vitamin
B-6 supplements. Infants or children who are diagnosed at an early age may
experience positive results from a low-methionine diet. It’s
believed that this diet helps to prevent some types of mental disabilities and
Even with treatment, you may experience serious complications.
You may be at risk for blood clots if you have high homocysteine levels
consistently. Make sure you follow your treatment plan and schedule regular
checkups with your doctor. This will help your doctor monitor your treatment
and help to prevent complications.
How Can I Keep My
Child from Getting Homocystinuria?
This disorder occurs as a result of genetic mutations. This can
make it challenging to prevent. You should consider going to a genetic
counselor if a history of homocystinuria runs in your family. Prospective
parents can use this method to analyze the risks of having a child who inherits
Requesting an intrauterine diagnosis of the disorder
is another possible way to prevent this condition. This requires testing a
culture of amniotic cells or villi for the presence of the genetic mutation.