Ehlers-Danlos syndrome, hypermobility type (HT-EDS) is the most frequent form of EDS (see this term), a group of hereditary connective tissue diseases, and is characterized by joint hyperlaxity, mild skin hyperextensibility, tissue fragility and extra-musculoskeletal manifestations.
Exact prevalence and annual incidence are unknown but prevalence estimates range from 1/5,000 to 1/20,000. These figures may however be underestimated due to clinical variability. Most affected patients are female.
Onset can be at any age but it is difficult to assess in young children due to higher joint laxity at this age. Wide clinical variability is found. The primary manifestation is hyperlaxity involving any joints: subluxations and dislocations are common and may occur spontaneously or following minor trauma. Hyperlaxity is more pronounced in younger patients and in females. Patients may also have soft or mildly hyperextensible skin, easy bruising and bleeding disorders. Gastrointestinal involvement with functional bowel disorders is common, while esophageal hypomobility, gastroesophageal reflux and gastritis are sometimes found. Complications often include chronic pain affecting physical activity, fatigue, sleep disorders, early osteoarthritis and osteoporosis, and cardiovascular symptoms (chest pain, palpitations, postural instability). In most cases, one or both parents of an affected individual have some degree of joint laxity, easy bruising, or soft skin, and some of these symptoms occasionally seem to segregate within the patient's family.
The underlying pathogenic mechanism is unknown. A small number of patients have been found to have haploinsufficiency of tenascin X, a glycoprotein expressed in connective tissues and encoded by the TNXB gene (6p21.3), which has also been found to be defective in the rare cases of autosomal recessive classic EDS (see this term).
Diagnosis is currently based on major and minor diagnostic criteria including clinical signs and family history as defined in the Villefranche classification. Major diagnostic criteria include joint hyperlaxity, soft skin or skin hyperextensibility, and an absence of other significant skin or soft tissue fragility. Supportive diagnostic criteria include a positive family history, recurrent joint instability, and easy bruising. However, the Villefranche classification does not take into account the extra-musculoskeletal manifestations. The currently available scoring criteria (Beighton score) have been demonstrated to be highly variable among investigators.
The main differential diagnosis is other types of EDS, particularly those characterized by significant connective tissue abnormalities. There is still debate as to whether benign joint hypermobility syndrome (BJHS) is a distinct disorder or part of a clinical continuum. Other diseases that also involve joint laxity are generally easy to distinguished from EDS by their characteristic features.
Prenatal testing is not available in the absence of an identified causal gene mutation.
Transmission is autosomal dominant. De novo events should be suspected if the parents of an affected patient have no signs of EDS. It is not known whether penetrance is complete but there is highly variable expressivity. Some cases may be autosomal recessive.
There is no specific treatment. Supportive and symptomatic individualized treatments include physical therapy, rehabilitation, assistive devices, pain medications, and suitable therapy for extra-articular manifestations. Surgical procedures should be considered with caution.
There is no increased risk of early mortality but high morbidity due to joint hyperlaxity, chronic and acute pain as well as extra-musculoskeletal manifestations which all greatly diminish quality of life.
Last update: September 2012