Ehlers Danlos Syndrome is a group of disorders of connective tissue that was formally identified in 1899 by Danish physician Edward Ehlers. Ehlers described patients that had characteristic symptoms including hyperflexible skin, lax joints and increased tendency of bruising. A few years later, Henri-Alexander Danlos, a French physician, published a paper describing similar symptoms. With the help of these two men, Ehlers-Danlos syndrome (EDS) became a formally recognized disease in the literature, although the cause of the new disease would not be understood for several decades (Parapia and Jackson, 2008).
While Ehlers and Danlos classified their syndrome as one single entity, Barabas (1967) identified that the disease has several different subtypes, with each displaying unique symptoms and clinical manifestations; this study notably identified several different forms of the disease, including the vascular form. There are currently six major subtypes of EDS, and all effect the synthesis or maintenance of collagen, a type of connective tissue. Collagen is the most abundant protein in the human body, and provides strength and structural integrity to nearly every cell; collagen is essential for the normal function of everything from bones and tendons to blood vessels. Although each subtype of EDS is surprisingly distinct, all patients share common symptoms including easily bruised skin and hyperflexible joints. All types of EDS are somewhat rare, affecting only 1:200,000 people (Malfait, 2010). The vascular type (vEDS), which is the most severe and has the highest mortality rate, is even more rare, affecting only a small percentage of EDS patients.
A landmark 1975 study identified that vascular EDS patients do not synthesize Type III collagen (Col3), and the authors showed that this lack of protein causes the symptoms identified nearly a century earlier by Ehlers and Danlos (Pope et al, 1975). The vascular type Ehlers Danlos Syndrome, previous called Type IV EDS, is extremely dangerous because it primarily affects collagen synthesis in blood vessels and abdominal organs. The inability to synthesize normal collagen makes these blood vessels and organs weak, and more susceptible to rupture, causing a potentially life-threatening hemorrhage.
With the dawn of the genetic revolution in the 1990s, some of the first mutations that cause vEDS were identified, and the disease was traced to the COL3A1 gene, which encodes Type III Collagen. Although initial studies hypothesized that Col3 was simply not produced, these newer experiments began to show that vEDS patients synthesize dysfunctional forms of Col3 (Smith et al, 1997). Only a year later, tests showed that vEDS mutations triggered the synthesis of smaller collagen precursors that were unable to form the triple-helix that is essential for Col3 stability and function (Superti-Furga et al, 1998). Over 300 mutations in this gene on chromosome 2q31 have since been documented, and all affect the production of collagen precursors that are vital to normal collagen function.
Together, these studies identified that the symptoms of vEDS were caused by the lack of functional collagen. Patients were simply not producing adequate Type III Collagen, and since collagen acts as a structural support for organs and blood vessels, these tissues were quite literally falling apart.
Type III Collagen obvious plays a crucial role in the body, and the COL3A1 gene, which is mutated in vEDS, encodes the precursors that form collagen. In a mechanism that is not well understood, three identical alpha-chains bind together and intertwine in a corkscrew-like shape to form one Col3 protein; individual precursor chains by themselves are nonfunctional. The Col3 homotrimer is functional, and can bind to other Col3 units, forming a long, flexible chain of collagen that is able to provide structural integrity and support to all the cells in the body.
Collagen Type III canonically plays a role in creating the extracellular matrix (ECM) of all cells, the small layer of support tissue seen in every organ and tissue in the body. Here, the protein’s role cannot be overstated, as the ECM surrounds nearly every cell in the body; although Col3 is present in the largest quantities in the intestines and arteries, it is also found in smaller amounts throughout the entire body. Col3 in the ECM provides structural support to the tissue and serves as an anchor, which prevents cells from moving and ensures consistent tissue organization (Smith et al 1997). Patients with vEDS lose this of structural support, which can be seen macroscopically with hyper-flexible joints and sunken facial features, as the collagen that normally supports these areas (i.e. various tendons and ligaments) is largely nonfunctional. The ECM is also vital to allowing the organ to perform its normal function; as but one example, the collagen in the ECM of the liver is required for proper detoxification and bile secretion, and to prevent liver fibrosis (Karsdal et al, 2015).
Col3 probably plays the largest role in major blood vessels, though, as it is a major component of arterial walls. These vessel walls need to be both elastic and extremely strong to accommodate the force of the contracting heart muscle. Interestingly, the very long collagen fibrils that can be seen microscopically in the walls are made up of both Col3 and Col1, and Col3 plays a major role in the development and organization of Col1. Col3 regulates the diameter of Col1 alpha-chains, which must be carefully controlled and kept uniform in order to ensure a symmetrical fiber; fibers that are too thin will be weak and overly flexible, and unable to perform their normal stabilization function (Liu et al, 1997). Correct fiber length is essential because Col1 is a major component in the walls of the aorta, the largest blood vessel in the body. Unsurprisingly, vEDS, which causes a deficiency in Col3, and thus causes downstream disregulation of Col1, increases the risk of aortic rupture, which is almost always fatal; both Col1 and 3 are essential to maintain the strength and elasticity of the aorta, as well as other major vessels in the body, like the femoral and carotid arteries (Vouyouka et al, 1999). Collagen does not play a major role in veins or smaller arteries, and these vessels are therefore not at increased risk of rupturing.
Beyond this structural role in the walls of arteries, Col3 also plays a major role in the healing process of skin, tendons, and bone. It is known, for example, that Col3 promotes regeneration of skin after a laceration, and inhibits the formation of scars by promoting the differentiation of myofibroblasts, which prevent scarring (Volk et al, 2011). In tendons and ligaments, Col3 is also able to increase healing by working to form small cross-links between broken cartilage fibers, which helps stabilize the repair site, thus speeding the healing process performed by other support cells (Liu et al, 1995). After bone breakage, collagen also plays a role in stimulating osteoblast activity, which secrete the organic material that is later mineralized into bone (Miedel et al, 2015).
Vascular rupture– Greatly increased propensity for arterial rupture. The collagen that normally supports and strengthens the walls of the vessels is not present, so these blood vessels are highly susceptible to breakage. Such breakage can be preceded by aneurysm, fistula, or dissection, which are irregularities and structural weaknesses in the wall of the vessel. Breakage of large blood vessels, like the aorta or carotid artery can cause massive internal hemorrhage, which is almost always deadly.
Organ rupture– Organs, notably the small and large intestines and uterus, are particular vulnerable to rupture, as these organs use large amounts of Col3 to maintain both elasticity and strength. In vEDS, such collagen is not present, so the organs are not as robust and strong, and thus are prone to physically bursting (Germain and Herrera-Guzman 2004). The rupture of an organ is a life-threatening emergency, as various materials (i.e. enzymes, acid, partially digested food) can leak out into the peritoneal cavity, causing destruction of neighboring tissues and massive infection. Organ rupture can occur in vEDS patients from a relatively small amount of force, so patients are generally advised to avoid contact supports and heavy exercise. During pregnancy, uterine rupture is somewhat common, especially during the final trimester as the large baby places enormous pressure on the mother’s organs and surrounding blood vessels.
Facial dysmorphia– Various symptoms including thin, pursed lips, lobe-less ears, pinched nose, and prominent eyes are some of the most obvious features of patients with vEDS. Such features can be useful for diagnostic purposes, but are not always present and are not exclusive to the disease.
Hyperextension of joints– Collagen normally is a component of cartilage, tendons, and ligaments, which all prevent the hyperextension and hyperflexion of joints, most notably the wrists, fingers, and knees. Since collagen levels are so low, the tendons and ligaments may become weakened or physically damaged, allowing the joints to move more freely beyond their normal range of motion, which can cause irreversible joint damage.
Decreased bone mass—Bone volume and density are reduced in vEDS patients, which is associated with weaker bones that are more “brittle,” and thus easily damaged and broken. Although it was always believed that collagen is not present in mature trabecular bones (bones in the arm and leg), it was recently shown that Col3 does play an important role in strengthening the bone. Those without Col3 have bones with less mineralization and fewer bone precursor cells (Volk, 2014).
Thin skin– the skin appears much thinner than normal and is somewhat translucent, allowing veins to be easily seen on the skin of the patient, especially on the thorax and shoulders. Skin also appears abnormally aged and wrinkled based on the expected skin characteristics for the patient’s true age (Germain and Herrera-Guzman, 2004).
Increased bruising– Patients with vEDS bruise easily and frequently. Since blood vessels are fragile and at risk of breakage, bruising occurs very easily, even from relatively minor injuries or insults. Such bruising is caused directly by the weaknesses in the vessels, rather than by clotting or platelet disorders (De Paepe and Malfait, 2004).
The rupture of organs and blood vessels is obviously associated with a high mortality rate, although the other symptoms of the disease are relatively mild, allowing vEDS patients to live a relatively normal and active life. Unfortunately, symptoms tend to worsen with time, as the aging body is unable to fully repair itself; the body of a younger patient is remarkably resilient and adaptive, and is usually able to function normally, even without normal collagen levels. Correspondingly, one study showed that 25% of patients will experience one major complication of the disease by age 20 (i.e. arterial, bowel, or other organ rupture) and 80% will have one complication by age 40; many of these complications are fatal, resulting in the decrease life expectancy seen in vEDS patients (Pepin et al, 2000).
Diagnosing vEDS can be particularly challenging due to the rarity of the disease. Few doctors are actively looking for, or even aware of, the vascular form of this disease. With the exception of organ or arterial rupture, most patients do not have severe enough symptoms to seek medical attention, and consequently many diagnoses are made post-mortem, after a vessel or organ ruptures. Vascular abnormalities tend to be found accidentally, such as during a routine ultrasound or from a CT scan in response to a medical problem not caused by vEDS; vascular weaknesses can generally be identified by an astute physician via MRI, CT, or ultrasound. Since collagen is generally not found in the blood and urine, these frequently used tests would not show the presence of vEDS. Anatomical abnormalities in the face, like a very thin nose, lobe-less ears and bulging eyes, may help alert a physician to the presence of vEDS, but these signs are not always extremely obvious.
The only definitive way to diagnose vEDS is to use genetic testing. Gene sequencing of the COL3A1 gene is required, and this can be compared to the normal sequence of Col3 available in online databases. Several hundred mutations that cause vEDS have already been reported in the literature, and a matching mutation in the literature would help confirm the diagnosis. Gene sequencing is rapidly becoming affordable, and this is the gold standard for diagnosis.
Collagen structure of vEDS patients can also be examined indirectly using SDS-Page gel electrophoresis, the method of choice before genetic testing was available. Mutant collagen has a different shape and molecular weight than normal collagen, which changes the speed in which the protein moves through the gel (Germain, 2007). While this does not necessarily indicate that the disease is vEDS, it can help to show abnormalities in collagen synthesis, which is caused by relatively few diseases, of which EDS is the most common. Today, though, this type of testing is less common, and is only used to confirm a mutation found via sequencing, or when showing that a newly discovered mutation in COL3A1 correlates with changes in collagen structure.
Recently, a new spectroscopic method was developed to determine the quality and quantity of collagen quality in bone that does not require gel electrophoresis. Bone with abnormal collagen has incorrect ratios of Carbon:Nitrogen, which can be detected using a newly discovered FT-Rama spectroscopy method (France et al, 2014). Although this method is not yet commonly being used in the clinic, it may serve as a useful tool to augment, rather than replace, existing diagnostic methods.