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Marfan syndrome

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Marfan syndrome
SpecialtyMedical genetics Edit this on Wikidata

Marfan syndrome is an autosomal dominant genetic disorder of the connective tissue characterized by unusually long limbs, great stature, or long toes (or fingers) in proportion to the person's 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. It is named after Antoine Marfan, the French pediatrician who first described it in 1899

Epidemiology

Marfan syndrome affects men and women in an equal manner,[1] as the mutation has no bias for gender or geographic location. Estimates indicate that approximately 60 000 (1 in 5000, or 0.02% of the population)[1] to 200 000[2] Americans have Marfan syndrome. Each parent with the condition has a 50% chance of passing it on to a child due to its autosomal dominant nature. Most individuals with Marfan syndrome have another affected family member, but approximately 15-30% of all cases are due to de novo genetic mutations[3] — such spontaneous mutations occur in about 1 in 20 000 births. Marfan syndrome is also an example of dominant negative mutation and haploinsufficiency[4][5]. It is associated with incomplete penetrance, therefore not all persons carrying the mutation develop the disease.

Pathogenesis

Marfan syndrome has been linked to a defect in the FBN1 gene on chromosome 15[6], which encodes a glycoprotein called fibrillin-1. Fibrillin is essential for the formation of the elastic fibers found in connective tissue, as it provides the scaffolding for tropoelastin[3]. Elastic fibers are found throughout the body but are particularly abundant in the aorta, ligaments and the ciliary zonules of the eye, consequently these areas are among the worst affected. Without the structural support provided by fibrillin many connective tissues are weakened, which can have severe consequences for 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. It has been found that simply reducing the level of normal fibrillin-1 causes a Marfan-related disease in mice[7].

Transforming growth factor beta (TGFβ) plays an important role in Marfan syndrome. Fibrillin-1 binds TGFβ and inactivates it. In Marfan syndrome, reduced levels of fibrillin-1 allow activated TGFβ to damage the lungs and heart. A defect in the gene TGFβR2 on chromosome 3, a receptor protein of TGFβ, has also been related to Marfan syndrome[8]. Marfan syndrome can often be confused with Loeys-Dietz syndrome, a similar connective tissue disorder resulting from mutations in the TGFβ receptor genes TGFβR1 and TGFβR2[9].

Diagnosis

Although genetic testing is available, a diagnosis is usually made solely on clinical findings. A clinical diagnosis is based on specific criteria that were established in 1996[10].

Symptoms

There are no signs or symptoms that are unique to Marfan syndrome. It is usually one sign or symptom that is apparent in an individual that leads doctors to look for other signs of the syndrome, and an eventual diagnosis. The connective tissue affected by Marfan syndrome is involved in diverse organs and tissues. Even in the same family, each affected individual might have a different combination of symptoms and a difference in severity.

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.

Eyes

Marfan syndrome can also seriously affect the eyes and vision. Nearsightedness or myopia and Astigmatism is common, but farsightedness can also be found in people with Marfan syndrome. Periodic eye exams of individuals with vision difficulties can lead to an ophthalmologist or optometrist discovering dislocation, or subluxation, of the crystalline lens in one or both eyes (ectopia lentis) by carefully observing these structures using a slit-lamp biomicroscope. This can be differentiated from the similar condition homocystinuria where the dislocation is inferonasal ,in marfans the dislocation is superotemporal. Sometimes, no eye problems are apparent until the weakening of connective tissue in the eye causes detachment of the retina.[11] Early onset glaucoma can be another complication.

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 aneurysm or even aortic dissection.

Lungs

Marfan syndrome 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. Marfan has also been associated with sleep apnea and idiopathic obstructive lung disease.

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 upright MRI of the lower spine. Dural ectasia that has progressed to the point of causing these symptoms would appear in a upright MRI image as a dilated pouch that is wearing away at the lumbar vertebrae.[11] Other spinal issues associated with Marfan include degenerative disk disease and spinal cysts.

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.[12] 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).[13] 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.

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.[14] Other medical treatments, as well as physical therapy, are also available.

Treatment of a spontaneous pneumothorax 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.

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.[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 early 2007, coordinated by Johns Hopkins. [16]

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

Well known people

Below is a list of prominent figures known or believed to have had Marfan syndrome:

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

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

Aortic aneurysm or dilitation Flat feet Obstructive lung disease
Arachnodactyly Gigantism Osteoarthritis
Bicuspid aortic valve Glaucoma Pectus carinatum or excavatum
Craniosynostosis Hernias Pneumothorax
Cysts Hypermobility of the joints Retinal detachment
Cystic medial necrosis Malocclusion Scoliosis
Dural ectasia Mitral valve prolapse Sleep apnea
Ectopia lentis Myopia Stretch marks

References

  1. ^ a b "The role of heredity and family history". National Marfan Foundation. 1999. Retrieved 2007-01-11.
  2. ^ "New, Deadly Relative of Marfan's Syndrome Discovered". MedicineNet.com. 2006. Retrieved 2007-01-11.
  3. ^ a b Cotran. Robbins Pathologic Basis of Disease. Philadelphia: W.B Saunders Company. 0-7216-7335-X. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ Judge, Daniel P. "Evidence for a critical contribution of haploinsufficiency in the complex pathogenesis of Marfan syndrome". The Journal of Clinical Investigation. 114 (2): 172–181. doi:10.1172/JCI200420641. PMID 15254584. Retrieved 2007-02-15. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Judge, Daniel P. (2005). "Marfan's syndrome". Lancet. 366 (9501): 1965–76. doi:10.1016/S0140-6736(05)67789-6. PMID 16325700. Retrieved 2007-02-15. {{cite journal}}: Check |doi= value (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ McKusick V (1991). "The defect in Marfan syndrome". Nature. 352 (6333): 279–81. PMID 1852198.
  7. ^ Lygia Pereira; et al. (1999). "Pathogenetic sequence for aneurysm revealed in mice underexpressing fibrillin-1". Proceedings of the National Academy of Sciences. 96 (7): 3819-3823. {{cite journal}}: Explicit use of et al. in: |author= (help)
  8. ^ Entrez Gene (2007). "TGFBR2 transforming growth factor, beta receptor II" (Entrez gene entry). NCBI. Retrieved 2007-01-11.
  9. ^ "Related Disorders: Loeys-Dietz". National Marfan Foundation. Retrieved 2007-01-11.
  10. ^ "1996 Revised Criteria for the Marfan Syndrome". Retrieved 2007-01-11.
  11. ^ a b "Marfan Syndrome". Mayo Clinic. Retrieved 2007-01-12.
  12. ^ "Heart Surgery for Marfan Syndrome". Mayo Clinic. Retrieved 2007-01-12.
  13. ^ "Overview of the Nuss Procedure for Pectus Excavatum". Children's Hospital of The King's Daughters. Retrieved 2007-01-12.
  14. ^ "Dural Ectasia in the Marfan Spine: Symptoms and Treatment". Scoliosis Research Society. Retrieved 2007-01-12.
  15. ^ Habashi, Jennifer P. (April 7, 2006). "Losartan, an AT1 Antagonist, Prevents Aortic Aneurysm in a Mouse Model of Marfan Syndrome". 312 (5770): 117–121. doi:10.1126/science.1124287. {{cite journal}}: Check date values in: |date= (help); Cite journal requires |journal= (help); External link in |news= (help); Unknown parameter |abstract= ignored (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |news= ignored (|newspaper= suggested) (help)
  16. ^ "Atenolol vs. Losartan in Individuals with Marfan Syndrome Clinial Trial". National Marfan Foundation. Retrieved 2007-01-12.
  17. ^ "Did Akhenaten Suffer from Marfan's Syndrome?". Canadian Marfan Association. Retrieved 2007-01-11.
  18. ^ "Flo Hyman". Volleyball Hall of Fame. Retrieved 2007-01-11.
  19. ^ "Marfan's Syndrome Is Deadly, Elusive". WNBC.com. Retrieved 2007-01-11.
  20. ^ Connel, David (September 2, 2006). "Retrospective blues: Robert Johnson—an open letter to Eric Clapton". British Medical Journal. 333 (7566): 489. Retrieved 2007-01-11. {{cite journal}}: Check date values in: |date= (help)
  21. ^ "NMF Mourns the Loss of its Honorary Co-Chair, Vincent Schiavelli". National Marfan Foundation. Retrieved 2007-01-11.
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