Connective Tissue Disorders

Connective tissue is one of four major types of tissue in the body. The four categories are connective, epithelial, muscle, and nervous tissue. Connective tissue includes all those tissues that hold organs together, such as blood, bone, cartilage, and fat.

There are many disorders of the connective tissue. Some connective tissue disorders (CTDs) are genetic, some are environmental, and some are idiopathic, meaning they do not have a known cause. Connective tissue fibers run through many organs, holding them together. These fibers are constructed of proteins including fibrillin, collagen, and elastin. As proteins are encoded by genes in the DNA, many genetic diseases affecting connective tissue proteins are found. Genetic CTDs include Ehlers-Danlos syndrome, affecting collagen; Marfan syndrome, affecting fibrillin; and Loeys-Dietz syndrome, typically affecting vascular fibrillin. An environmentally caused CTD is scurvy, which is a disruption of the collagen due to a lack of Vitamin C in the diet. Cancer of a connective tissue is classified as a sarcoma. Some CTDs can have an autoimmune component; that is, the person's body forms antibodies against its own tissue. The antibodies attack native tissue, leading to inflammation, pain, and sometimes other debilitating symptoms.

Common CTDs include soft tissue diseases, or soft tissue rheumatic syndromes. These disorders afflict the tissues surrounding joints; therefore, the cushioning and mobility functions of the joints may be impaired. Most soft tissue rheumatic syndromes are types of tendonitis. These soft tissue diseases are generally caused by strain, injury, or overuse of a particular joint or muscle.

Blood disorders can stem from absent or aberrant abilities to synthesize, mature, or break down blood cells. These disorders may affect red or white blood cells, plasma, platelets, or blood enzymes. A common blood disorder is anemia, which is a reduced amount of blood cells. Many types of anemia can be found; some are genetic, some are nutritional, and others are idiopathic. A famous although very rare blood disease is hemophilia, which is usually found in males. Hemophilia is genetically caused by two main genetic mutations in important blood clotting factors. Hemophiliacs (people with hemophilia) have blood that fails to clot properly; therefore, small cuts or nosebleeds do not heal quickly and severe blood loss can result. Each type of hemophilia is classified as mild, moderate, or severe, depending on how much clotting factor is present in the blood.

Bone disorders can be diseases that affect the bone directly, cancer of the bone, or side effects of other cancers. Osteogenesis imperfecta (OI), also know as “brittle bone disease” is a genetic CTD affecting the bones. Another bone CTD, avascular necrosis (AN) is a result of inadequate or completely absent blood supply to the bone. An injury or trauma may have cut off the blood supply; the result is a starved bone that may die. The most common site for AN is at the end of a long bone.

Cartilage is also a connective tissue. The three types of cartilage are elastic cartilage, fibrocartilage, and hyaline cartilage. Elastic cartilage is so named because it contains elastin, a yellow-tinted protein. Fibrocartilage can endure high amounts of pressure; thus, it is found between the vertebrae. Hyaline cartilage is named for its glassy appearance. It lubricates joints, among other physiological roles. Because there are multiple forms of cartilage, each with distinct properties and functions, there are many forms of CTDs that affect cartilage.

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