Ehlers-Danlos syndrome is a group of disorders that affect connective tissues, which are tissues that support the skin, bones, blood vessels, and other organs. Defects in connective tissues cause the signs and symptoms of Ehlers-Danlos syndrome, which vary from mildly loose joints to life-threatening complications. See also connective tissue disorders.
In the past, there were more than 10 recognized types of Ehlers-Danlos syndrome. In 1997, researchers proposed a simpler classification that reduced the number of major types to six and gave them descriptive names: the arthrochalasia type, the classic type, the dermatosparaxis type, the hypermobility type, the kyphoscoliosis type, and the vascular type. Other forms of the condition may exist, but they have been reported only in single families or are not well characterized.
Although all types of Ehlers-Danlos syndrome affect the joints and many also affect the skin, features vary by type. An unusually large range of joint movement (hypermobility) occurs with most forms of Ehlers-Danlos syndrome, particularly the hypermobility type. Infants with hypermobile joints often appear to have weak muscle tone, which can delay the development of motor skills such as sitting, standing, and walking. The loose joints are unstable and prone to dislocation, chronic pain, and early-onset arthritis. Dislocations involving both hips are a characteristic finding in infants with the arthrochalasia type of Ehlers-Danlos syndrome.
Many people with Ehlers-Danlos syndrome have soft, velvety skin that is highly elastic and fragile. Affected individuals tend to bruise easily, and some types of the condition also cause abnormal scarring. People with the classic form of Ehlers-Danlos syndrome experience wounds that split open with little bleeding and leave scars that widen over time to create characteristic shallow "cigarette paper" scars. The dermatosparaxis type of the disorder is characterized by skin that sags and wrinkles. Extra (redundant) folds of skin may be present as affected children get older.
Some forms of Ehlers-Danlos syndrome, notably the vascular and kyphoscoliosis types, can involve serious and potentially life-threatening complications. Blood vessels can tear (rupture) unpredictably, causing internal bleeding, stroke, and shock. The vascular type of Ehlers-Danlos syndrome is also associated with an increased risk of organ rupture, including tearing of the intestine and rupture of the uterus (womb) during pregnancy. People with the kyphoscoliosis form of Ehlers-Danlos syndrome experience severe, progressive curvature of the spine that can interfere with breathing.
Occurrence of Ehlers-Danlos syndrome
Although it is difficult to estimate the overall frequency of Ehlers-Danlos syndrome, the combined prevalence of all types of this condition may be about 1 in 5,000 individuals worldwide. The hypermobility and classic forms are most common; the hypermobility type may affect as many as 1 in 10,000 to 15,000 people, while the classic type probably occurs in 1 in 20,000 to 40,000 people.
Other forms of Ehlers-Danlos syndrome are very rare. About 30 cases of the arthrochalasia type and fewer than 60 cases of the kyphoscoliosis type have been reported worldwide. About a dozen infants and children with the dermatosparaxis type have been described. The vascular type is also rare; estimates vary widely, but the condition may affect about 1 in 250,000 people.
Inheritance of Ehlers-Danlos syndrome
The inheritance pattern of Ehlers-Danlos syndrome varies by type. The arthrochalasia, classic, hypermobility, and vascular forms of the disorder usually have an autosomal dominant pattern of inheritance. Autosomal dominant inheritance means that one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from one affected parent. Other cases result from new (sporadic) gene mutations. These cases occur in people with no history of the disorder in their family.
The dermatosparaxis and kyphoscoliosis types of Ehlers-Danlos syndrome, and some cases of the classic and hypermobility forms, are inherited in an autosomal recessive pattern. In autosomal recessive inheritance, two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.