Disorders of the skeleton

The evil that men do lives after them; the good is oft interred with their bones.

William Shakespeare. Act 3, scene ii, Julius Caesar.

Bone in the body is a living tissue performing many functions in addition to providingmechanical support for the body. It is composed of a hard matrix of minerals (such as calcium and potassium salts) deposited around protein fibres (such as collagen).

In the developing foetus, the skeleton is first laid down as cartilage which is then replaced by bone. Bone X-rays, especially in young children, will still show areas of cartilage present at the ends of growing bones; this can be used to estimate a child’s age. However, even in adulthood, the size and shape of bones change, and are continuously being remodelled in response to everyday stresses. In fact, the entire human skeleton is replaced every 10 years, through the activities of bone-dissolving and bone-rebuilding cells. 

Skeletal defects are common birth abnormalities and can be caused by a variety of different genes leading to more than 200 distinct diseases.

Decreased bone or cartilage growth usually leads to disproportionate short-stature - this differs to proportionate short stature for example seen in growth hormone deficiency. Depending upon which bones are primarily affected, such as in the limbs, trunk, or ribs, it is possible to differentiate by a glance some of the various types of disproportionate short-stature, and in some cases which gene might be involved, e.g. achondroplasia, pseudoachondroplasia, cartilage-hair hypoplasia, spondyloepiphyseal dysplasia congenita, Ellis-van-Creveld syndrome, and primodial dwarfism).

Increased bone growth can lead to the bones becoming more brittle and in sever cases can lead to short disproportionate stature, deformed bone growth and increased fractures, e.g. osteopetrosis.

Deranged bone growth can in severe cases lead to massive deformity, e.g. Craniodiaphyseal dysplasia, Klippel-Feil syndrome, fibrodysplasia ossificans progressiva and sclerosteosis.