Marfan Syndrome (cont.)
What causes Marfan syndrome?
Marfan syndrome is caused by a
defect (mutation)
in the gene that
determines the structure of fibrillin, a protein that is an important part
of connective tissue. A person with Marfan syndrome is born with the
disorder, even though it may not be diagnosed until later in life. Although
everyone with Marfan syndrome has a defect in the same gene, the mutation is
specific to each family and not everyone experiences the same
characteristics to the same degree. This is called variable expression,
meaning that the defective gene expresses itself in different ways in
different people. Scientists do not yet understand why variable expression
occurs in people with Marfan syndrome.
The defective gene can be inherited: The child of a person who has Marfan
syndrome has a 50 percent chance of inheriting the disease. Sometimes a new
gene defect occurs during the formation of sperm or egg cells, but two
unaffected parents have only a 1 in 10,000 chance of having a child with
Marfan syndrome. Possibly 25 percent of cases are due to a spontaneous
mutation at the time of conception.
How Marfan syndrome diagnosed?
There is no specific laboratory test, such as a blood test or skin biopsy, to
diagnose Marfan syndrome. The doctor and/or geneticist (a doctor with special
knowledge about inherited diseases) relies on observation and a complete medical
history, including
- information about any family members who may have the
disorder or who had an early, unexplained heart-related death
- a thorough physical examination, including an
evaluation of the skeletal frame for the ratio of arm/leg size to trunk size
- an eye examination, including a "slit lamp" evaluation
- heart tests such as an echocardiogram (a test that uses ultrasound waves to
examine the heart and aorta).
The doctor may diagnose Marfan syndrome if the
patient has a family history of the disease and there are specific problems in
at least two of the body systems known to be affected. For a patient with no
family history of the disease, at least three body systems must be affected
before a diagnosis is made. Moreover, two of the systems must show clear signs
that are relatively specific for Marfan syndrome.
In some cases, a genetic analysis may be useful, but such analyses are often
time consuming and may not provide any additional helpful information. Family
members of a person diagnosed with Marfan syndrome should not assume they are
not affected if there is no knowledge that the disorder existed in previous
generations of the family. After a clinical diagnosis of a family member, a
genetic study might identify the specific mutation for which a test can be
performed to determine if other family members are affected.
Next: What types of doctors treat
Marfan syndrome? »
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