Dwarfism is a physical disorder characterized by a small stature, of less than 4 feet 10 inches (147 cm). There are nearly 200 causes of dwarfism and the symptoms of this condition vary widely, depending on the cause. The medical term for dwarfism is restricted growth.
Restricted growth may be classified in several ways. Firstly, there are two main forms of the condition and these are described below:
Disproportionate dwarfism (DSS)
In DSS, some parts of the body are of normal size or larger than normal, while others are small. This is a result of abnormal bone growth. In most cases, it is the trunk that is of an average size and the limbs that are short, but the opposite can occur. The head may be disproportionately large compared with the body size. The majority of dwarfism cases are of the DSS type and the most common cause of DSS is a condition called achondroplasia.
Proportionate short stature (PSS)
In PSS, all parts of the body are small but they are in proportion to each other. Disorders that cause PSS affect overall growth and several bodily symptoms are often poorly developed. Usually, the cause of PSS is simply being born to small parents.
Another cause of PSS is growth hormone deficiency, caused by the pituitary gland failing to produce sufficient levels of growth hormone. Signs of this condition include slow growth rate for age, delayed or absent sexual development, and height below the third percentile. Some genetic conditions can also cause PPS. Girls with Turner syndrome and people with a condition called SHOX gene haplo-insufficiency have mild PSS.
Location and tissue affected
The disorders that cause dwarfism are classified according to the location of the affected body parts or the type of tissue affected. The names of these disorders are therefore usually based on the following:
- Rhizomelic - Bones of the upper arm or thigh are affected
- Mesomelic - Bones of the forearm or lower leg are shortened
- Acromelic - Bones of the hands and feet are affected
- Micromelic - Entire limbs are shortened
- Osteo - The bone is affected, e.g. osseous dysplasia, osteochondrodystrophy
- Chondro - The cartilage is affected, e.g. achondroplasia, chondrodystrophy, osteochondrodystrophy.
- Spondylo - The vertebrae are affected
Reviewed by Sally Robertson, BSc