Ehlers-Danlos Syndrome

Updated: Jun 09, 2016
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Dirk M Elston, MD  more...
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Overview

Background

Ehlers-Danlos syndrome (EDS) is the name given to a group of more than 10 different inherited disorders; all involve a genetic defect in collagen and connective-tissue synthesis and structure.

Ehlers-Danlos syndrome can affect the skin, joints, and blood vessels. This syndrome is clinically heterogeneous; the underlying collagen abnormality is different for each type. Clinical recognition of the types of Ehlers-Danlos syndrome is important. One type, type IV, is associated with arterial rupture and visceral perforation, with possible life-threatening consequences.

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Pathophysiology

Ehlers-Danlos syndrome is a heterogeneous group of inherited connective-tissue disorders characterized by joint hypermobility, cutaneous fragility, and hyperextensibility. The collagen defect has been identified in only 6 of the 11 types of Ehlers-Danlos syndrome. Type IV is characterized by a decreased amount of type III collagen. It is autosomal dominant and caused by mutations in the COL3A1 gene that result in increased fragility of connective tissue with arterial, intestinal, and uterine ruptures and premature death. [1] Types V and VI are characterized by deficiencies in hydroxylase and lysyl oxidase, an important posttranslational modifying enzyme in collagen biosynthesis. Type VII has an amino-terminal procollagen peptidase deficiency. Type IX has abnormal copper metabolism. Type X has nonfunctioning plasma fibronectin.

In Ehlers-Danlos syndrome types I and II, the classic variety, identifying the molecular structure in most individuals who are affected is difficult. Causative mutations may involve the COL5A1, COL5A2, and tenascin-X genes and are implied to be in the COL1A2 gene. Nonetheless, in most families with autosomal dominant Ehlers-Danlos syndrome, the disease appears to be linked to loci that contain the COL5A1 or COL5A2 genes. Although half of the mutations that cause Ehlers-Danlos syndrome types I and II are likely to affect the COL5A1 gene, a significant portion of the mutations result in low levels of mRNA from the mutant allele as a consequence of nonsense-mediated mRNA decay. [2]

Bouma et al evaluated 3 generations in a family with Ehlers-Danlos syndrome type II. The genomic defect was an A(-2)→G substitution at the exon 14 splice-acceptor site. Transmission electron micrographs of type I collagen fibrils in a proband dermal biopsy specimen demonstrated heterogeneity in fibril diameter that was greater than that of a matched control sample. The proband was found to have a greater proportion of both larger and smaller fibrils, and occasional fibrils with a cauliflower configuration were observed. [3]

Wenstrup and associates identified haploinsufficiency of the COL5A1 gene that encodes the proalpha1(V) chain of type V collagen in the classic form of Ehlers-Danlos syndrome. Eight of 28 probands with classic Ehlers-Danlos syndrome who were heterozygous for expressed polymorphisms in COL5A1 had complete or nearly complete loss of expression of one COL5A1 allele. One third of individuals with classic Ehlers-Danlos syndrome were estimated to have mutations of COL5A1 that result in haploinsufficiency. These findings suggest that the normal formation of the heterotypic collagen fibrils that contain types I, III, and V collagen requires the expression of both COL5A1 alleles. [4] Type V collagen mutations are pivotal in classic Ehlers-Danlos syndrome. [5]

Autosomal recessive–type VI Ehlers-Danlos syndrome, also known as the kyphoscoliotic type, is characterized by neonatal kyphoscoliosis, generalized joint laxity, skin fragility, and severe muscle hypotonia at birth. Biochemically, this type is attributed to a deficiency in lysyl hydroxylase (LH), the enzyme that hydroxylates specific lysine residues in the collagen molecule to form hydroxylysines with 2 important functions. The residues are attachment sites for galactose and glucosylgalactose, and they act as precursors of the cross-linking process that gives collagen its tensile strength.

More than 20 mutations are identified in the LH1 gene that contributes to LH deficiency and clinical Ehlers-Danlos syndrome type VI. Yeowell and Walker identified 2 of these mutations in 5 or more unrelated patients: (1) a large duplication of exons 10-16, which arise from a homologous recombination of intronic Alu sequences, and (2) a nonsense mutation, Y511X, in exon 14 of the LH1 gene. Both mutations seem to originate from a single ancestral gene. [6]

Tenascin-X is a large extracellular matrix protein, a deficiency of which causes a clinically distinct recessive form of this syndrome. [7] Thus, factors other than collagens or collagen-processing enzymes may cause this syndrome. This newly described form may be associated with additional anomalies.

A case with colonic perforation in a young girl, with a fatal outcome, was related to a novel mutation of the COL3A1 gene. Crystal structure of human type III, in the structure G991-G1032 cystine knot, shows both 7/2 and 10/3 symmetries. [8]

A novel point mutation has been found in the vascular type of Ehlers-Danlos syndrome. The mutation took place in the second position of exon 24 of COL3A1. [9]

Impaired wound healing is a typical feature of Ehlers-Danlos syndrome, probably for a fibroblast defect. Wound repair can be achieved using exogenous type V collagen. [10]

Ehlers-Danlos syndrome pediatric patients have been shown to have deficiencies in 3 genes of the glutathione S-transferase family (GSTM1, GSTT1, GSTP1). This leads to the generation of reactive oxygen species. [11]

Reduced activity of beta4-galactosyltransferase 7 (beta4GalT-7) is associated with the progeriform Ehlers-Danlos syndrome.

Biallelic mutations in FKBP14 may result in a recessive form of Ehlers-Danlos syndrome with progressive kyphoscoliosis, myopathy, hearing loss, and, possibly, an increased risk for vascular complications. [12]

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Epidemiology

Frequency

The prevalence of Ehlers-Danlos syndrome is reported to be 1 case in approximately 400,000 people, but mild or incomplete forms appear to be underdiagnosed and more common than other forms.

Race

No racial predominance seems to exist; however, some believe that whites probably are affected more than other races.

Sex

The sex-related prevalences are almost equal.

Age

The disease has clinical features (eg, joint mobility, skin extendibility, scarring tendency) that are easily recognizable beginning in early childhood. The other clinical manifestations require more time to become evident. Ehlers-Danlos syndrome is usually diagnosed in young adults.

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Prognosis

Type IV Ehlers-Danlos syndrome is a severe form. Patients often have a shortened lifespan because of the spontaneous rupture of a large artery (eg, splenic artery, aorta) or the perforation of internal organs. Surgery can pose life-threatening risks in these patients. [13] Arterial aneurysms, valvular prolapse, and spontaneous pneumothorax are common complications. The prognosis with this type is poor. Sudden death can occur after visceral perforation or after the rupture of a large vessel, most commonly an abdominal and splenic vessel.

The other types are usually not as dangerous, and affected individuals can live a healthy if somewhat restricted life. Type VI is also somewhat dangerous, although it is rare.

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Patient Education

For excellent patient education resources, visit eMedicineHealth's Skin Conditions and Beauty Center. Additionally, see eMedicineHealth's patient education article Bruises.

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