Connective Tissue

Connective tissue forms the supportive framework of the vertebrate body. Although variable in amount and composition from one organ system to another, a common feature of all connective tissues is the prominent presence of extracellular matrix (ECM) within which several types of connective tissue cells are embedded.

ECM is composed of a variety of glycoproteins that assemble into a complex, organized meshwork. Until recently, the ECM was thought to serve mainly as a relatively inert scaffold providing support and stabilisation to the different tissues. It is now clear that the matrix plays a far more active and complex role in regulating the behavior of the cells that contact it, influencing their development, migration, proliferation, shape and function. In most connective tissues, ECM glycoproteins are secreted by fibroblasts but also other members of the fibroblast family, such as chondroblasts (in cartilage) and osteoblasts (in bone) express matrix components.

Two main classes of structural protein components are found within the ECM : (1) proteoglycans, which are glycoproteins, covalently linked to polysaccharide chains, and (2) fibrous proteins (e.g. collagen, elastin, fibronectin, etc.) which have both structural and adhesive functions. Whereas the proteoglycans in connective tissue form a gel-like structure which resists compressive forces on the matrix and allows rapid diffusion of nutrients, metabolites and hormones between the blood and the tissue cells, the fibrous proteins resist stretching forces by collagen fibers and provide resilience by the rubberlike elastin fibers.

Heritable connective tissue diseases are caused by mutations in genes responsible for the synthesis of the different glycoprotein components, in genes involved in enzymatic modifications of these glycoproteins, or in genes which play a role in the organisation or homeostasis of the ECM. Several of those diseases are associated with specific symptoms in the skin.

Disease type/subtype

Cutis laxa, hereditary

Ehlers-Danlos syndrome, arthrochalasis type

Ehlers-Danlos syndrome, classic type

Ehlers-Danlos syndrome, dermatosparaxis type

Ehlers-Danlos syndrome, hypermobility type

Ehlers-Danlos syndrome, kyphoscoliotic type

Ehlers-Danlos syndrome, unclassified variants

Ehlers-Danlos syndrome, vascular type

Lipoid proteinosis

Pseudoxanthoma Elasticum