Marfan syndrome

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Marfan syndrome is a genetic connective tissue disorder often characterized by unusually long limbs [tall stature], and/or long toes and/or fingers in proportion to height. The disease may also affect numerous other structures and organs — including the lungs, eyes, heart, blood vessels, dural sac surrounding the spinal cord, and hard palate &mdash. It is named after Antoine Marfan, the French pediatrician who first described it in 1896.

Marfan syndrome
Classifications and external resources
OMIM 154700
DiseasesDB 7845
MedlinePlus 000418
eMedicine ped/1372  orthoped/414

Contents

[edit] Cause

Marfan syndrome is an autosomal dominant disorder that has been linked to a defect in the FBN1 gene on chromosome 15[1]. FBN1 codes for a protein called fibrillin-1, which is essential for the formation of elastic fibers found in connective tissue. Marfan syndrome is also an example of a dominant negative mutation. Marfan syndrome is associated with incomplete penetrance, therefore not all persons carrying the mutation develop the disease. Without the structural support provided by fibrillin, many connective tissues are weakened, which can have severe consequences on support and stability. A related disease has been found in mice, and the study of mouse fibrillin synthesis and secretion, and connective tissue formation, has begun to further our understanding of Marfan syndrome in humans. For instance it has been found that simply reducing the level of normal fibrillin-1 causes the Marfan related disease in mice [2].

Transforming growth factor beta (TGFβ) plays an important role in Marfan syndrome. Fibrillin-1 binds TGFβ, inactivating it. In Marfan syndrome, reduced levels of fibrillin-1 allow TGFβ to damage the lungs and heart. A defect in TGFβR2 gene on chromosome 3, a receptor protein of TGFβ, has also been related to Marfan syndrome.[3] Marfan syndrome can often be confused with Loeys-Dietz syndrome, a highly similar connective tissue disorder resulting from mutations in the TGFβ receptor genes TGFβR1 and TGFβR2.[4]

[edit] Diagnosis

Although genetic testing is available, a diagnosis is usually made solely on clinical findings. A clinical diagnosis uses specific criteria that were established in 1996.[5]

[edit] Epidemiology

Because Marfan syndrome is caused by an autosomal dominant genetic defect, each parent with the condition has a 50 percent chance of passing it on to a child. Most individuals with Marfan syndrome have another affected family member, but about 1/4 to 1/3 of all cases are due to de novo genetic mutations. Such spontaneous mutations occur in about 1 in 20,000 births. Estimates indicate that perhaps anywhere from 60,000 (1 in 5,000; 0.02 percent of the population)[6] to 200,000[7] Americans have Marfan syndrome. It affects all races and both sexes equally.[8]

[edit] Symptoms

The symptoms of Marfan syndrome can affect diverse organs and tissues. Each individual affected may have a different combination of symptoms that vary in severity.

[edit] Skeletal system

The most readily visible signs may be associated with the skeletal system. Many individuals with Marfan syndrome grow to larger than normal height, and have long, slender limbs, fingers, and toes. An individual's arms can be disproportionately long compared to his or her height. In addition to affecting height and limb proportions, Marfan syndrome can produce other skeletal signs. Abnormal curvature of the spine (scoliosis) is common, as is abnormal indentation (pectus excavatum) or protrusion (pectus carinatum) of the sternum. Other signs include abnormal joint flexibility, a high mouth palate, the need for orthodontics work, flat feet, stooped shoulders, and unexplained stretch marks on the skin. Some people with Marfans have speech impediments as a result of the high palates and small jaws.

[edit] Eyes

Marfan syndrome can also affect the eyes. Nearsightedness or myopia is a common in people with Marfan syndrome. Periodic eye exams of individuals with vision difficulties can lead to an opthalmologist discovering dislocation of the optic lens in one or both eyes (ectopia lentis) using a slit-lamp test. Sometimes, no eye problems are apparent until the weakening of connective tissue in the eye causes detachment of the retina.[9]. Early onset glaucoma can be another complication. The lenses are frequently displaced (ectopia lentis).

[edit] Cardiovascular system

The most serious conditions associated with Marfan syndrome primarily involve the cardiovascular system. Undue fatigue, shortness of breath, heart palpitations, racing heart beats, or pain in the left chest, back, shoulder, or arm, can bring an individual into the doctor's office. A heart murmur heard on a stethescope, an abnormal reading on an electrocardiogram, or symptoms of angina can lead a doctor to order an echocardiogram. The echocardiogram can reveal signs of leakage or prolapse of the mitral or aortic valves that control the flow of blood through the heart. However, the major sign that would lead a doctor to consider an underlying condition is a dilated aorta or an aortic aneurysm. Sometimes, no heart problems are apparent until the weakening of the connective tissue in the ascending aorta causes an aortic dissection or even a rupture of the aorta.

[edit] Lungs

Marfan snydrome is a risk factor for spontaneous pneumothorax. In spontaneous unilateral pneumothorax air escapes from a lung and occupies the pleural space between the chest wall and a lung. The lung becomes partially compressed or collapsed. This can cause pain, shortness of breath, and it can cause cyanosis and even death, if not treated. Treatment is dependant on the volume of air in the pleural space and the natural progression of the individual's condition. A small pneumothorax might resolve without active treatment in 1 to 2 weeks. Recurrent pneumothoraxes might require chest surgery. Moderately sized pneumothoraxes might need chest drain management for several days in hospital. Large pneumothoraxes are likely to be medical emergencies requiring emergency decompression. Marfan has also been associated with sleep apnea and idiopathic obstructive lung disease.

[edit] Central nervous system

Another condition that can reduce the quality of life for an individual, though not life-threatening, is dural ectasia, the weakening of the connective tissue of the dural sac, the membrane that encases the spinal cord. Dural ectasia can be present for a long time without producing any noticeable symptoms. Symptoms that can occur are lower back pain, leg pain, abdominal pain, other neurological symptoms in the lower extremeties, or headaches. Such symptoms usually diminish when the individual lies flat on his or her back. These types of symptoms might lead a doctor to order an X-ray of the lower spine. Dural ectasia is usually not visible on an X-ray in the early phases. A worsening of symptoms and the lack of finding any other cause should eventually lead a doctor to order a vertical MRI of the lower spine. Dural ectasia that has progressed to the point of causing these symptoms would appear in a vertical MRI image as a dilated pouch that is wearing away at the lumbar vertebrae.[10]. Other spinal issues associated with Marfan include degenerative disk disease and spinal cysts; because Marfan may cause spinal abnormalities that are asymptomatic, any spinal surgery contemplated on a Marfan patient should only follow detailed imaging and careful surgical planning, regardless of the indication for surgery.

[edit] Management

There is no cure for Marfan syndrome, but life expectancy has increased significantly over the last few decades. The syndrome is treated by addressing each issue as it arises, and, in particular, considering prophylactic medication [even for young children] to slow progression of aortic dilation.

Regular checkups by a cardiologist are needed to monitor the health of the heart valves and the aorta. The goal of treatment is to slow the progression of aortic dilation and damage to heart valves by eliminating arrythmias, minimizing the heart rate, and minimizing blood pressure. Beta blockers have been used to control arrythmias and slow the heart rate. Other medications might be needed to further minimize blood pressure without slowing the heart rate, such as ACE inhibitors and angiotensin II receptor antagonists, also known as angiontensin receptor blockers (ARBs). If the dilation of the aorta progresses to a significant diameter aneurysm, causes a dissection or a rupture, or failure of the aortic or other valve, surgery, possibly a composite aortic valve graft (CAVG) or valve-sparing procedure, becomes necessary. Although aortic graft surgery (or any vascular surgery) is a serious undertaking it is generally successful if undertaken on an elective basis. Surgery in the setting of acute aortic dissection or rupture is considerably more problematic. Elective aortic valve/graft surgery is usually considered when aortic root diameter reaches 50 millimetres, but each case needs to be specifically evaluated by a qualified cardiologist. New valve-sparing surgical techniques are becoming more common.[11] As Marfan patients live longer, other vascular repairs are becoming more common, e.g. repairs of descending thoractic aortic aneurysms and aneurysms of vessels other than the aorta.

The skeletal and ocular manifestations of Marfan syndrome can also be serious, although not life-threatening. These symptoms are usually treated in the typical manner for the appropriate condition. This can also affect height, arm length, and life span. The Nuss procedure is now being offered to people with Marfan syndrome to correct 'sunken chest' or (pectus excavatum).[12]

Clinical trials have been conducted of the drug acetazolamide in the treatment of symptoms of dural ectasia. The treatment has demonstrated significant functional improvements in some sufferers[13]. Other medical treatments, as well as physical therapy, are also available.

Research in laboratory mice has suggested that the angiotensin II receptor antagonist losartan (marketed by Merck & Co, Inc. as Cozaar), which appears to block TGF-beta activity, can slow or halt the formation of aortic aneurysms in Marfan syndrome.[14][15] A large clinical trial sponsored by the National Institutes of Health comparing the effects of losartan and atenolol on the aortas of Marfan patients is scheduled to begin in late 2006, coordinated by Johns Hopkins. [16]

Genetic counseling and specialized clinics are available at many academic medical centers for affected persons and family members.

[edit] Well known people

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Below is a list of prominent figures known or believed to have had Marfan syndrome (most are according to the U.S. [National Marfan Foundation] [17]:

[edit] Related disorders

The following disorders have similar signs and symptoms of Marfan syndrome:

The following conditions that can result from having Marfan syndrome can also occur in people without any known underlying disorder:

[edit] External links

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