I have only mentioned Marfan Syndrome in passing for a few old posts, like the one about Abraham Lincoln, but I wanted to focus on Marfan’s Syndrome at the more deep and detailed level here.

First, “What is Marfan Syndrome?”

From Wikipedia (HERE)… Again I will highlight the most important parts.

Marfan syndrome (also called Marfan’s syndrome) is a genetic disorder of the connective tissue. People with Marfan’s tend to be unusually tall, with long limbsand long, thin fingers.

The syndrome is inherited as a dominant trait, carried by the gene FBN1, which encodes the connective protein fibrillin-1. People have a pair of FBN1 genes. Because it is dominant, people who have inherited one affected FBN1 gene from either parent will have Marfan syndrome.

Marfan syndrome has a range of expressions, from mild to severe. The most serious complications are defects of the heart valves and aorta. It may also affect the lungs, the eyes, the dural sac surrounding the spinal cord, the skeleton and the hard palate.

In addition to being a connective protein that forms the structural support for tissues outside the cell, the normal fibrillin-1 protein binds to another protein,transforming growth factor beta (TGF-β). TGF-β has deleterious effects on vascular smooth muscle development and the integrity of the extracellular matrix. Researchers now believe, secondary to mutated fibrillin, excessive TGF-β at the lungs, heart valves, and aorta weakens the tissues and causes the features of Marfan syndrome. Since angiotensin II receptor antagonists (ARBs) also reduce TGF-β, ARBs (losartan, etc.) have been tested in a small sample of young, severely affected Marfan syndrome patients. In some patients, the growth of the aorta was indeed reduced.

Signs and symptoms

The constellation of long limbs, dislocated lenses and the aortic root dilation are generally sufficient to make the diagnosis of Marfan syndrome with reasonable confidence. More than 30 other clinical features are variably associated with the syndrome, most involving the skeleton, skin, and joints. Considerable clinical variability occurs within families carrying the identical mutation.

Skeletal system

Most of the readily visible signs are associated with the skeletal system. Many individuals with Marfan syndrome grow to above-average height. Some have long, slender limbs (dolichostenomelia) with long fingers and toes (arachnodactyly). An individual’s arms may be disproportionately long, with thin, weak wrists. In addition to affecting height and limb proportions, Marfan syndrome can produce other skeletal anomalies. Abnormal curvature of the spine (scoliosis), abnormal indentation (pectus excavatum) or protrusion (pectus carinatum) of the sternum are not uncommon. Other signs include abnormal joint flexibility, a high palate, malocclusions, flat feet, hammer toes, stooped shoulders, and unexplained stretch marks on the skin. It can also cause pain in the joints, bones and muscles in some patients. Some people with Marfan have speech disorders resulting from symptomatic high palates and small jaws. Early osteoarthritis may occur.

Pathogenesis

Marfan syndrome is caused by mutations in the FBN1 gene on chromosome 15, which encodes the glycoprotein fibrillin-1, a component of the extracellular matrix. Fibrillin-1 protein is essential for the proper formation of the extracellular matrix, including the biogenesis and maintenance of elastic fibers. The extracellular matrix is critical for both the structural integrity of connective tissue, but also serves as a reservoir for growth factors. Elastin 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.

A transgenic mouse has been created carrying a single copy of a mutant fibrillin-1, a mutation similar to that found in the human gene known to cause Marfan syndrome. This mouse strain recapitulates many of the features of the human disease and promises to provide insights into the pathogenesis of the disease. Reducing the level of normal fibrillin 1 causes a Marfan-related disease in mice.

Transforming growth factor beta (TGFβ) plays an important role in Marfan syndrome. Fibrillin-1 directly binds a latent form of TGFβ, keeping it sequestered and unable to exert its biological activity. The simplest model of Marfan syndrome suggests reduced levels of fibrillin-1 allow TGFβ levels to rise due to inadequate sequestration. Although it is not proven how elevated TGFβ levels are responsible for the specific pathology seen with the disease, an inflammatory reaction releasing proteases that slowly degrade the elastin fibers and other components of the extracellular matrix is known to occur. The importance of the TGFβ pathway was confirmed with the discovery of the similar Loeys-Dietz syndrome involving the TGFβR2 gene on chromosome 3, a receptor protein of TGFβ. Marfan syndrome has often been confused with Loeys-Dietz syndrome, because of the considerable clinical overlap between the two pathologies.

Diagnosis

Diagnostic criteria of Marfan syndrome were agreed upon internationally in 1996. A diagnosis of Marfan syndrome is based on family history and a combination of major and minor indicators of the disorder, rare in the general population, that occur in one individual — for example: four skeletal signs with one or more signs in another body system such as ocular and cardiovascular in one individual. The following conditions may result from Marfan syndrome, but may also occur in people without any known underlying disorder.

Epidemiology

Marfan syndrome affects males and females equally, and the mutation shows no ethnic or geographical bias. Estimates indicate about one in 3,000 to 5,000 individuals have Marfan syndrome. Each parent with the condition has a 50% risk of passing the genetic defect on to any child due to its autosomal dominant nature. Most individuals with Marfan syndrome have another affected family member — approximately 15–30% of all cases are due to de novo genetic mutations—such spontaneous mutations occur in about one in 20,000 births. Marfan syndrome is also an example of dominant negative mutation and haploinsufficiency. It is associated with variable expressivity; incomplete penetrance has not been definitively documented.