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In 1991, scientists identified the altered gene that causes Marfan syndrome. The gene is located on a region of chromosome 15 and known as the fibrillin-1 (FBN-1) gene. Most patients with Marfan exhibit a mutation of this gene. Some, however, do not, and another gene has been implicated in those cases of Marfan.
Although researchers have located the genetic mutation associated with Marfan, there is no screening test that can conclusively diagnose Marfan. This is because the gene involved is also associated with many other inherited disorders of the connective tissue. These include Beals syndrome, Ehlers-Danlos syndrome, Hajdu Cheney syndrome and Stickler syndrome. To complicate matters further, the syndrome manifests itself differently in each patient, meaning that expensive prenatal genetic testing is a poor indicator of the severity of the resulting Marfan syndrome.
Instead of relying on genetic testing, physicians have developed criteria to diagnose Marfan. These criteria rely on the presence of numerous conditions associated with Marfan. Tests that may be used to diagnose the conditions associated with Marfan include:
- Skeletal exam. A physical examination of the appearance and shape of the patient’s skeletal structure with specific focus on the spine. A tall, thin frame with with long arms, legs and fingers are also assoicated with this condition. In addition, the patiend will be examined for excessively loose or flexible joints.
- Auscultation. The physician will listen to the heart through a stethoscope to detect whether there are abnormal sounds, such as a heart murmur.
- Family medical history. As complete a record as possible of the conditions and diseases of close family members across several generations.
- Echocardiogram. A sound wave image of the heart that allows a physician to see the structure of the heart and aorta. It can assess the size of the heart, valve function and the motion of the heart walls. An echocardiogram is the most common test used to track Marfan patients.
- Slit-lamp exam. An eye exam using a specialized lamp that can detect lens dislocation. The eyes will also be examined for severe near-sightedness, detached retina and early glaucoma or cataracts.
- CAT scan (computed axial tomography) of the chest to assess the thoracic aorta.
If an individual does not have a first-degree relative with Marfan syndrome, a positive diagnosis can be made if the patient has a major manifestation in two body systems and involvement of a third system. The third manifestation cna be either a major or minor factor. A first-degreee relative refers to one's parent, sibling or child.
However, if the patient has the genetic mutation associated with Marfan, two body systems, including one major system, need to be affected for a Marfan diagnosis.
Because symptoms of the syndrome may not become apparent until adulthood, it is vital that parents with Marfan have their children checked regularly for signs of the disease. In newborn infants, an evaluation would include:
- Skeletal measurements such as lengths of the total body, upper and lower body, arm span, legs, hands and fingers. The spine is examined for signs of curvature and the joints for signs of laxity or contracture.
- Eye exam for lens dislocation, abnormal reflexes, or iridonesis (an uneven shimmering of the iris).
- Cardiovascular exam for heart murmur, mitral valve prolapse and/or aortic regurgitation.
- An echocardiogram to assess the valves and aortic size.
This newborn evaluation can help to diagnose Marfan early. However, signs and symptoms may develop over time, so periodic re-evaluations are recommended. | 
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