If you’ve read my page ‘What is EDS?‘ you’ll have learned that there are 7 main types of Ehlers-Danlos. Each type is a distinct disorder and can be traced to a slightly different mutation relating to the production or usage of collagen within the body with the exception of the Hypermobile Type for which the faulty gene has as yet has not been isolated. EDS types “run true” in a family. This means that an individual with Vascular EDS will not normally have a child with Classical Type EDS.
EDS types are defined according to the signs and symptoms that are manifested, in a set of major and minor diagnostic criteria for each type. I have included the table of criteria further down this post.
The seven main types are:
- Classical (old types I & II)
This type is distinguished by it’s extensive skin involvement. Marked skin hyperextensibility (stretchy skin), soft velvety texture with widened paper-like scars and joint hypermobility. When all diagnostic criteria are met this type is 90% due to a mutation in type 5 collagen. Some people however have a clinical diagnosis of Classical type and have an as yet unknown gene.
- Hypermobile (old type III/3)
The most common form of Ehlers-Danlos, most people with EDS have this type. It’s not actually all that rare but it is very much mis &under-diagnosed.
Joint hypermobility is the dominant symptom in this type with recurring subluxations and dislocations being common. Skin may have some mild involvement eg. velvety texture and easy bruising but is rarely as stretchy as in the Classical Type. Many patients suffer chronic pain. This type when severe is frequently disabling and can produce milder forms of the symptoms more usually associated with other types.
No genetic cause has been located as yet but the syndrome however a small sub-population of less than 10% have been shown to have Tenascin-X deficiency (TNXB gene). Hypermobile Type is inherited following a dominant pattern.
There is some discussion in the medical community as to whether Joint Hypermobility Syndrome may be a milder form of Hypermobile EDS. I agree that some patients with a JHS diagnosis almost certainly do have EDS but others really do not. They have acquired or bio-mechanical hypermobility meaning the JHS diagnosis is still required. Doctors just need to learn to separate out those with connective tissue problems from those without.
- Vascular (old type IV/4)
This is generally regarded as the most serious form of EDS and is the only form of EDS that can affect life expectancy. Arterial/venous and organ fragility is the hallmark of this type and unfortunately many people do not discover that they have it until they suffer a serious rupture or worse. This type often has few outward signs other than extensive bruising after only minor traumas and thin skin which reveals the pattern of the vasculature. Clinicians used to think that Vascular type patients all had a particular look to them but as more people have been diagnosed this has turned out not to be true (information from Dr. Brad Tinkle). This type is caused by mutations on the gene for type 3 collagen.
- Kyphoscoliosis (old type VI/6)
This type is marked out by a progressive scoliosis, sufferers are hypermobile and often have extremely low muscle tone from birth which can affect gross motor skills. This type is the result of a deficiency of lysylhydroxylase (caused by a mutation on the PLOD gene) which is a collagen-modifying enzyme and is inherited in a recessive pattern.
- Arthrochalasia (old type VIIa&b/7a&b)
This type is marked out by congenital (at birth) bilateral (both sides) hip dislocation and short stature. Generalised hypermobility with recurrent subluxations and dislocations, scoliosis and skin manifestations.Individuals with this type are very rare, there are less than 50 known cases worldwide, it is caused by mutations to type 1 collagen.
- Dermatosparaxis (old type VIIc/7c)
This type is characterised by sagging, redundant skin. The skin is very fragile but wounds heal normally unlike in the Classical Type. Patients bruise very easily. This is another very rare type with not many cases reported worldwide. It is caused by a mutation on the ADAMTS-2 gene which produces pro-collagen peptidase, an enzyme that aids in the processing of type I pro-collagen.
Since the types were last classified at Villefranche in 1997 some more types have been described but their names are not yet official and there are no set diagnostic criteria to help doctors diagnose them.
Examples of these syndromes include progeroid type (B4GALT7 gene), musculocontractural type (CHST14 gene) and spondylocheirodyplastic type.
Prior to 1997 the types were classified with numbers shown as roman numerals rather than names, some people and doctors still use these old classification numbers.
I hope this post has been helpful in explaining the wide variety of EDS types. Each type can be expressed on a spectrum from mild through to severe. Why some patients are more greatly affected than others is sometimes due to the form of their mutation as in the Vascular type but is usually unknown.
If you have any questions please do pop them in the comments and I’ll do my best to answer them but remember I am just a patient not a doctor or geneticist!