Muscles, bones, cartilage, ligaments, and tendons are built mostly of connective tissue. Connective tissue is also found in other parts of the body, such as the skin and internal organs. Connective tissue is strong and thus able to support weight and tension (see Biology of the Musculoskeletal System: Tendons and Bursas).
There are over 200 disorders that involve connective tissue. Some of these disorders have no clear cause, and some are genetically inherited. Certain hereditary disorders cause connective tissue throughout the body to form abnormally. In general, hereditary connective tissue disorders develop in childhood but last throughout life. Most hereditary connective tissue disorders are diagnosed by their symptoms and findings during a physical examination. Analysis of genes, usually from a blood test, may help doctors diagnose some hereditary disorders. A biopsy (removal of a tissue sample for examination under a microscope) can also help. The tissue is usually removed using a local anesthetic, which numbs the area. X-ray studies can reveal bone abnormalities that may be associated with a connective tissue disorder.
Resource: Merck Manual Home Edition