There are many conditions and diseases that can cause short stature, dwarfism. Some of these conditions involve a bone disorder — the bones do not grow and develop normally. These conditions are called skeletal dysplasias or chondrodystrophies. People with these conditions of short stature often refer to themselves as dwarfs, little people, or short-statured persons. More than 100 skeletal dysplasias have been discovered. Of these, achondroplasia is the most common. It occurs in all races and with equal frequency in males and females, but is a rare disease.
An individual with achondroplasia has disproportionate short stature, which means the head is large and the arms and legs are short compared, to the chest. This shortness is particularly noticeable in the upper arms and thighs. Other signs are a large forehead, a flat or even depressed area at the base of the nose, a protruding jaw, and sometimes the teeth are crowded and the upper and lower teeth may be badly aligned. An adult with achondroplasia usually has an exaggerated forward curve to the lower spine. The legs of a person with achondroplasia almost always become bowed and the elbows often cannot be straightened completely. Sometimes the person has limited twisting ability at the elbows. The hands are short, and the feet are short and flat. Another sign is double jointedness, caused by loose ligaments in some joints. Achondroplastic children can flex their finger, wrist, hip, and knee joints to an extreme degree because of this. These signs are usually apparent at birth, and achondroplasia can be diagnosed at that time. Affected men average 51.8 inches in height, while women average 48.6 inches. There is no relationship between the height of the parents and the adult height of their children with achondroplasia.
Children with achondroplasia develop slower. It takes them along time to gain proper head control, because of the extremely large head the neck muscles have to be strong enough to support it. Children with achondroplasia commonly get middle-ear infections in the first five or six years of life, probably due to abnormal drainage of the tube from the middle ear to the throat. Weight control is a frequent and lifelong problem for many people with this disorder. Both children and adults must be careful of what they eat because they are prone to add excess weight. The basic cause is faulty development of the bone structure. If these infections are not recognized and treated, or are resistant to treatment, the child may sustain significant hearing loss. Dental problems caused by overcrowding of teeth (especially those of the upper jaw) may occur. Malocclusion often results and makes good oral hygiene difficult. In addition to ordinary dental care, orthodontic treatment may be necessary. The large head seen in achondroplasia is often confused with hydrocephalus (“water on the brain”). Hydrocephalus may develop in achondroplasia, but it rarely requires surgical treatment. It is important to measure the young child’s head circumference regularly to distinguish hydrocephalus from normal head growth. Young children with achondroplasia are at increased risk for specific neurologic and respiratory problems. These result from smaller openings in the skull, particularly at the foramen magnum (or “large window”) at the base of the skull. In some cases, surgery is required to enlarge this opening and relieve pressure on the base of the brain and spinal cord. Common orthopedic problems in childhood include a reverse curvature (kyphosis) of the lower spine in infancy, and bowed legs, which may develop any time after children begin to walk. The spinal kyphosis usually resolves without treatment, but may require bracing or surgery if it persists. Bowed legs may be treated by bracing or orthopedic surgery. Older children and adults frequently experience fatigue, numbness, or pain in the lower back and thighs. Often these complaints are simple muscular problems that do not require special care. If they are persistent or severe, the person should be evaluated by a physician, perhaps a neurologist. Nerve or spinal-cord problems are common because of the narrow spinal canal, particularly in the lower back.
Mutations within a single gene cause achondroplasia. The condition may be passed from one generation to the next or it may result from a new mutation in a