About 30,000 dwarfs - people whose short stature is caused by a medical condition - live in the United States.

Although many dwarfs prefer the term “little people,” “dwarf” is appropriate, said Dr. Tamison Jewett, a clinical geneticist and pediatrician at Wake Forest University Baptist Medical Center.

“When I first started working in this job 16 years ago, I used to avoid that word. I thought it sounded pejorative. That is not true. Little people refer to themselves as dwarfs,” Jewett said.

Dwarfism can be the result of a malfunction of the pituitary gland, chromosomal abnormalities, malnourishment in the womb or after birth, or kidney disease, which caused the short stature of actor Gary Coleman. But most cases are genetic, said Jewett. Some forms of dwarfism cause medical problems; some also affect intellectual development. More than 200 causes for dwarfism have been documented.

When most people think of dwarfs, they think of small people whose bodies are not in proportion. Peter Dinklage, who starred in The Station Agent, and Warwick Davis, a veteran of the Star Wars movies who is currently appearing in Harry Potter and the Order of the Phoenix, are dwarfs. Both actors have a form of skeletal dysplasia; their bones did not grow and develop normally.

Although dwarfism is covered under the Americans With Disabilities Act, the disability is often more social than medical. Because of their size, dwarfs face challenges and must develop ways to cope with everyday chores that most of us do without thinking.

Historically, dwarfs have often been depicted as fanciful or humorous creatures - munchkins or leprechauns - or they have been depicted as sideshow freaks or objects of humor. The popular TV series Little People, Big World paints a more realistic picture of dwarfs as ordinary people who lead productive lives.

The TLC series follows dwarf parents Matt and Amy Roloff, and their four children, only one of whom is a dwarf. The show, which is now showing in sporadic reruns, is scheduled to begin its new season this fall at its regular time slot, 8 p.m. on Mondays.

The most common form of dwarfism is achondroplasia, a genetic form that affects growth in the long bones of the legs and arms. Achondroplasia, which experts say occurs once in 10,000 to 40,000 births, accounts for about 80 percent of all cases of dwarfism. The disparate numbers are based on various reports from different registries, Jewett said. She considers the incidence to be about one in 15,000 births.

Most cases of achondroplasia are caused by a spontaneous mutation in sperm or egg cells, which results in dwarf children being born to parents of average height. In other instances, the children inherit the already mutated gene from one or both parents.

People with achondroplasia can become parents of dwarfs and average-size children.

A child of two achondroplastic parents has a 25 percent chance of being average size and a 50 percent chance of being a dwarf. The child also has a 25 percent chance of inheriting two copies of the dwarfism gene. Those children are born with very small chest cages, underdeveloped lungs and the inability to breathe normally. They rarely survive.

Dwarfs with achondroplasia have a distinctive look that most people associate with dwarfism. Their arms and legs are disproportionately short, compared to their average-sized trunks, and their legs are sometimes bowed. Their heads are often disproportionately large, with depressed nasal bridges and prominent foreheads, Jewett said. Their hands show a natural division between the third and fourth fingers, similar to the Vulcan salute given by Dr. Spock in Star Trek.

Achondroplastic babies are at risk of sudden death because they often have a smaller-than-usual hole at the base of the skull where the spinal cord passes through, Jewett said. The spinal cord can become pinched at the neck. As many as 7 percent of children with achondroplasia die in infancy because of this problem, Jewett said. Those deaths do not fall under the umbrella of Sudden Infant Death Syndrome (SIDS), which results in unexplained cases of crib death.

As achondroplastic dwarfs age, the space around the spinal cord in their lower backs can narrow, causing leg pain, weakness and numbness.

Achondroplastic dwarfs can also have bowing of the long bones of the legs, sometimes severe enough to cause problems with walking. Little People, Big World covered the surgery that Zach Roloff, an achondroplastic dwarf like his mother, had to straighten one of his legs.

Another form of dwarfism known as SED (spondyloepiphyseal dysplasia congenital) occurs about once in every 95,000 births. This form can cause medical problems such as clubfeet and clef palate. Jewett said that people with SED usually have prominent eyes, cheekbones that are not well-developed and tend toward nearsightedness that can progress to retinal detachment. They can have short trunks and barrel chests.

Diastrophic dysplasia occurs about once in 110,000 births. Diastrophic dwarfs tend to have shortened forearms and calves and can have serious orthopedic problems requiring repeated surgeries. They are often born with clubfeet and can often have dislocation of the hips and various finger abnormalities.

“They have a characteristic appearance to their thumb, called a “hitchhiker” thumb,” Jewett said. The thumb stands away from the rest of the hand.

Children whose dwarfism is the result of metabolic or hormonal imbalances can be treated with hormone injections that will help them grow. The only treatment that can increase the height of people who have achondroplasia or diastrophic dysplasia is a painful procedure known as limb-lengthening. Doctors break the leg bones and slowly pull them apart as new bone fills in the gaps. The procedure can add as much as a foot to the height of a dwarf if it is done during childhood.

The surgery remains controversial in the dwarf community.

“Most of them believe, ‘This is the way I’m made, the way I am,’” Jewett said.

“There are others who really don’t want to be little. They feel uncomfortable being little and think, ‘I want to gain as much as I can.’”

■ Janice Gaston can be reached at 727-7364 or at jgaston@wsjournal.com.