The condition of being abnormally short or small, dwarfism has numerous causes. Some of these are hereditary, but all concern hormone disturbances, bone or deficiency diseases, and/or organ dysfunction. Two ailments--achondroplasia and pituitary dwarfism--are the most common causes of dwarfism.

Achondroplasia is a condition in which the development of cartilage, and therefore bone, is disturbed. The disorder appears in approximately one in every 10,000 births. The bones (especially those in the limbs) do not grow as long as they should, and simultaneously become abnormally thick. The bones in the trunk of the body and the skull are mostly unaffected, although the skull opening through which the spinal cord passes (foramen magnum) is often narrower than normal, and the opening through which the spinal cord runs (spinal canal) becomes abnormally small as it goes down the length of the spine.

Achondroplasia is caused by a genetic defect. It is...