Dwarfism is a condition of short stature. It is defined by the advocacy group Little People of America (LPA) as an adult height of 4 feet 10 inches or under, as a result of a medical or genetic condition. Although other groups may extend the criteria for certain forms of dwarfism to 5 feet, the average height of an adult with dwarfism is 4 feet.
There are two main categories of dwarfism -- disproportionate and proportionate. Disproportionate dwarfism is characterized by an average-size torso and shorter arms and legs or a shortened trunk with longer limbs. In proportionate dwarfism, the body parts are in proportion but shortened.
Dwarfism can be caused by any of more than 200 conditions. Causes of proportionate dwarfism include metabolic and hormonal disorders such as growth hormone deficiency.
The most common types of dwarfism, known as skeletal dysplasias, are genetic. Skeletal dysplasias are conditions of abnormal bone growth that cause disproportionate dwarfism.
Achondroplasia. The most common form of dwarfism, achondroplasia occurs in about one out of 26,000 to 40,000 babies and is evident at birth. People with achondroplasia have a relatively long trunk and shortened upper parts of their arms and legs. Other features of achondroplasia include:
- a large head with a prominent forehead
- a flattened bridge of the nose
- protruding jaw
- crowded and misaligned teeth
- forward curvature of the lower spine
- bowed legs
- flat, short, broad feet
Spondyloepiphyseal dysplasias (SED). A less common form of dwarfism, SED affects approximately one in 95,000 babies. Spondyloepiphyseal dysplasia refers to a group of conditions characterized by a shortened trunk, which may not become apparent until a child is between ages 5 and 10. Other features can include:
- club feet
- cleft palate
- severe osteoarthritis in the hips
- weak hands and feet
- barrel-chested appearance
Diastrophic dysplasia. A rare form of dwarfism, diastrophic dysplasia occurs in about one in 100,000 births. People who have it tend to have shortened forearms and calves (this is known as mesomelic shortening).
Other signs can include
- deformed hands and feet
- limited range of motion
- cleft palate
- ears with a cauliflower appearance
Skeletal dysplasia is caused by a genetic mutation. The gene mutation can occur spontaneously or can be inherited.
Diastrophic dysplasia and usually spondyloepiphyseal dysplasias are inherited in a recessive manner. This means a child must receive two copies of the mutated gene -- one from the mother, one from the father -- to be affected.
Achondroplasia, on the other hand, is inherited in a dominant manner. That means a child needs only one copy of the mutated gene to have that form of skeletal dysplasia. There is a 25% chance that a child born to a couple in which both members have achondroplasia will be of normal height. But there is also a 25% chance the child will inherit both dwarfism genes, a condition known as double-dominant syndrome. This is a fatal condition that usually results in miscarriage.
Often parents of children with achondroplasia do not carry the mutated gene themselves. The mutation in the child occurs spontaneously at the time of conception.
Doctors do not know what causes a gene to mutate. It is a seemingly random occurrence that can happen in any pregnancy. When average-size parents have a child with dwarfism due to a spontaneous mutation, it is not likely that other children will also have the mutation.
In addition to genetic skeletal dysplasia, short stature has other causes, including disorders of the pituitary, which influence growth and metabolism; kidney disease; and problems that affect the body's ability to absorb nutrients.
Some forms of dwarfism are evident in utero, at birth or during infancy and can be diagnosed through X-rays and a physical exam. A diagnosis of achondroplasia, diastrophic dysplasia, or spondyloepiphyseal dysplasia can be confirmed through genetic testing. In some cases, prenatal testing is done if there is concern for specific conditions.
Sometimes dwarfism doesn't become evident until later in a child's life, when dwarfism signs lead parents to seek a diagnosis. Here are signs and symptoms to look for in children that indicate a potential for dwarfism:
- a larger head
- late development of certain motor skills, such as sitting up or walking
- breathing problems
- curvature of the spine
- bowed legs
- joint stiffness and arthritis
- lower back pain or numbness in the legs
- crowding of teeth
Early diagnosis and treatment can help prevent or lessen some of the problems associated with dwarfism. People with dwarfism related to growth hormone deficiency can be treated with growth hormone.
In many cases, people with dwarfism have orthopaedic or medical complications. Treatment of those can include:
- Insertion of a shunt to drain excess fluid and relieve pressure on the brain
- A tracheotomy to improve breathing through small airways
- Corrective surgeries for deformities such as cleft palate, club foot, or bowed legs
- Surgery to remove tonsils or adenoids to improve breathing problems related to large tonsils, small facial structures, and/or a small chest
- Surgery to widen the spinal canal (the opening through which the spinal cord passes) to relieve spinal cord compression
Other treatment may include:
- Physical therapy to strengthen muscles and increase joint range of motion
- Back braces to improve curvature of the spine
- Placement of draining tubes in the middle ear to help prevent hearing loss due to repeated ear infections
- Orthodontic treatment to relieve crowding of teeth caused by a small jaw
- Nutritional guidance and exercise to help prevent obesity, which can aggravate skeletal problems