PRIMER The Ehlers–Danlos syndromes Fransiska Malfait1 ✉ , Marco Castori2, Clair A. Francomano3, Cecilia Giunta4, Tomoki Kosho5 and Peter H. Byers6 Abstract | The Ehlers–Danlos syndromes (EDS) are a heterogeneous group of hereditary disorders of connective tissue, with common features including joint hypermobility, soft and hyperextensible skin, abnormal wound healing and easy bruising. Fourteen different types of EDS are recognized, of which the molecular cause is known for 13 types. These types are caused by variants in 20 different genes, the majority of which encode the fibrillar collagen types I, III and V, modifying or processing enzymes for those proteins, and enzymes that can modify glycosaminoglycan chains of proteoglycans. For the hypermobile type of EDS, the molecular underpinnings remain unknown. As connective tissue is ubiquitously distributed throughout the body, manifestations of the different types of EDS are present, to varying degrees, in virtually every organ system. This can make these disorders particularly challenging to diagnose and manage. Management consists of a care team responsible for surveillance of major and organ-specific complications (for example, arterial aneurysm and dissection), integrated physical medicine and rehabilitation. No specific medical or genetic therapies are available for any type of EDS. The Ehlers–Danlos syndromes (EDS) comprise a genet­ six EDS types, denominated by a descriptive name6. The ically heterogeneous group of heritable conditions that most recent classification, the revised EDS classification in share several clinical features, such as soft and hyper­ 2017 (Table 1) identified 13 distinct clinical EDS types that extensible skin, abnormal wound healing, easy bruising are caused by alterations in 19 genes7. Of note, research 1Center for Medical Genetics, and joint hypermobility. Additional clinical features that published after the 2017 classification has described Ghent University Hospital, Ghent, Belgium. differ among EDS subtypes include fragility of soft tis­ another genetically distinct EDS type, provisionally clas­ sues, vessels and hollow organs, and involvement of the sified as classical­like EDS type 2 (clEDS2), bringing the 2Division of Medical Genetics, (REF.8) Fondazione IRCCS–Casa musculoskeletal system, all of which can result in chronic total number of EDS­associated genes to 20 . The Sollievo della Sofferenza, and severe disability and/or early mortality, and may affect extended 2017 classification (which includes clEDS2) San Giovanni Rotondo, the quality of life (QOL) of patients and their families. guides the clinical diagnosis, genetic confirmation, Foggia, Italy. Edvard Ehlers and Henri­Alexandre Danlos were management and genetic counselling of EDS. 3Department of Medical and dermatologists who, in the early twentieth century, Most EDS types that have a known genetic cause Molecular Genetics, Indiana described patients with joint hypermobility, excessive result from pathogenetic variants in genes encoding University School of Medicine, Indianapolis, IN, USA. skin extensibility, easy bruising and abnormal scar for­ fibrillar collagens types I, III and V, modifying or pro­ 1,2 4Connective Tissue Unit, mation after injury . Several years before their descrip­ cessing enzymes for these collagens, or enzymes that Division of Metabolism and tion, patients with similar manifestations were described have key roles in the biosynthesis of the glycosamino­ Children’s Research Centre, by Chernogubow in Russia, where his name is still used glycan (GAG) chains of proteoglycans. These molecules University Children’s Hospital, to describe what we refer to as classical EDS (cEDS)3. contribute to the physical properties of the extracellu­ Zurich, Switzerland. Frederick Park­Weber suggested that the condition be lar matrix (ECM) in essentially all tissues and organs. 5 Department of Medical called ‘Ehlers–Danlos syndrome’4. Since then, individu­ Despite the advances in gene identification, some Genetics, Shinshu University School of Medicine, als with the shared clinical features discussed above and patients have clinical features that are compatible with Matsumoto, Japan. with additional clinical findings have been classified into EDS but do not fit within a currently defined type and 6Department of Pathology the different EDS types; however, the classification has have no pathogenetic variants in the known EDS causa­ and Division of Medical changed over time with the discovery of the genetic basis tive genes, which indicates that the genetic heterogeneity Genetics, Department of these conditions. The 1986 ‘Berlin Nosology’ recog­ of EDS has not been completely resolved. of Medicine, University nized 11 types of EDS, which were defined by Roman Next­generation sequencing analysis and the abil­ of Washington, Seattle, WA, USA. numerals and which were based on clinical findings, mode ity to sequence all relevant genes at once has facilitated 5 ✉e-mail: fransiska.malfait@ of inheritance and biochemical alterations . After the elu­ timely and cost­effective genetic diagnosis of EDS, and ugent.be cidation of the biochemical and/or molecular basis of sev­ has refined the phenotypic spectra associated with https://doi.org/10.1038/ eral of these types, a revised classification, the ‘Villefranche pathogenetic variants in these genes. Definitive diag­ s41572-020-0194-9 Nosology’ was published in 1998, which recognized nosis of EDS relies on genetic confirmation, with the NATURE REVIEWS | DISEASE PRIMERS | Article citation ID: (2020) 6:64 1 0123456789(); PRIMER Table 1 | The 2017 international Ehlers–Danlos syndrome classification EDS type Gene (encoded Major clinical criteria Minor clinical criteria (abbreviation) protein) Disorders of collagen primary structure and collagen processing Classical (cEDS)a COL5A1 (α1(V) Skin hyperextensibility with atrophic scarring and Easy bruising, soft doughy skin, skin procollagen chain) generalized joint hypermobility fragility (or traumatic splitting), molluscoid pseudotumours (bluish-grey, COL5A2 (α2(V) spongy nodules, which are herniations procollagen chain) of subcutaneous fat, seen over easily traumatized areas), subcutaneous spheroids, COL1A1 ( 1(I) α hernia (or history thereof), epicanthal procollagen chain: folds, complications of joint hypermobility p.Arg312Cys (rare)) (such as sprain, (sub)luxation, pain, flexible flatfoot), family history of a first-degree relative who meets criteria Vascular (vEDS)a COL3A1 (α1(III) Family history of vEDS with documented Bruising unrelated to identified trauma procollagen chain) pathogenetic variant in COL3A1, arterial and/or in unusual sites such as cheeks and rupture at young age, spontaneous sigmoid back, thin, translucent skin with increased COL1A1 (α1(I) colon perforation in the absence of known colon venous visibility, characteristic facial features procollagen chain: disease, uterine rupture during third trimester (large eyes, periorbital pigmentation, small p.Arg312Cys (rare), of pregnancy, carotid-cavernous sinus fistula chin, sunken cheeks, thin nose and lips and p.Arg574Cys (rare), (in the absence of trauma) lobeless ears), spontaneous pneumothorax, p.Arg1093Cys (rare)) acrogeria, talipes equinovarus, congenital hip dislocation, small joint hypermobility, tendon and muscle rupture, gingival recession and gingival fragility, early-onset varicose veins Arthrochalasia COL1A1 (α1(I) Congenital bilateral hip dislocation, severe Muscle hypotonia, kyphoscoliosis, (aEDS)a procollagen chain) generalized joint hypermobility with multiple radiologically mild osteopenia, tissue COL1A2 (α2(I) dislocations, skin hyperextensibility fragility including atrophic scars, easy procollagen chain) bruising Dermatosparaxis ADAMTS2 (ADAMTS2, Extreme skin fragility with congenital or Soft and doughy skin texture, skin (dEDS)b N-proteinase) postnatal tears, craniofacial features (large hyperextensibility, atrophic scars, fontanel, puffy eyelids, excessive peri-orbital generalized joint hypermobility, skin, downslanting palpebral fissures, blue complications of visceral fragility (e.g. rectal sclerae, hypoplastic chin), progressively prolapse, bladder or diaphragm rupture), redundant, almost lax skin with excessive delayed motor development, osteopenia, skin folds at wrists and ankles, increased hirsutism, tooth abnormalities, refractive palmar wrinkling, severe bruisability with errors, strabismus risk of subcutaneous haematoma, umbilical hernia, postnatal growth retardation with short limbs, perinatal complications related to tissue fragility Cardiac valvular COL1A2 (α2(I) Severe progressive cardiac valvular insufficiency, Inguinal hernia, pectus deformity, joint (cvEDS)b procollagen chain (total skin involvement, joint hypermobility (generalized dislocations, foot deformities (pes planus, absence)) or restricted to small joints) pes planovalgus and hallux valgus) Disorders of collagen folding and collagen crosslinking Kyphoscoliotic PLOD1 (lysyl Congenital muscle hypotonia, congenital or For both genetic causes: skin (kEDS-PLOD1 hydroxylase 1) early-onset kyphoscoliosis, generalized joint hyperextensibility, easy bruising, or kEDS-FKBP14 hypermobility with (sub)luxations rupture/aneurysm of medium-sized artery, depending on the FKBP14 (FKBP22) osteopenia/osteoporosis, blue sclerae, causative mutation)b umbilical or inguinal hernia, pectus deformity, marfanoid habitus, talipes equinovarus, refractive errors. For PLOD1 mutations: skin fragility, microcornea, characteristic craniofacial features. For