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What is Dwarfism?

Definition of Dwarfism

Dwarfism is a medical or genetic condition that usually results in an adult height of four feet ten or shorter, among both men and women, although in some cases a person with a dwarfing condition may be slightly taller than that. By far the most frequently diagnosed cause of short stature is achondroplasia, a genetic condition that results in disproportionately short arms and legs. The average height of adults with achondroplasia is four feet.

According to information compiled by the Greenberg Center at Johns Hopkins Medical Center and by the late Lee Kitchens, a past president of Little People of America, the frequency of occurrence of the most common types of dwarfism is as follows:

  1. Achondroplasia (one per 26,000 to 40,000 births)
  2. SED (one per 95,000 births)
  3. Diastrophic dysplasia (one per 110,000 births)

These conditions are essentially untreatable, although some people with achondroplasia and hypochondroplasia have undergone painful (and controversial) limb-lengthening surgery.

Proportionate dwarfism -- that is, a short-stature condition that results in the arms, legs, trunk, and head being the same size in relation to each other as would be expected with an average-sized person -- is often the result of a hormonal deficiency, and may be treated medically. This condition is commonly referred to as growth-hormone deficiency.

Although achondroplasia accounts for perhaps 70 percent of all cases of dwarfism, there are approximately 200 diagnosed types, and some individuals with dwarfism never receive a definitive diagnosis.

Other genetic conditions that result in short stature include spondyloepiphyseal dysplasia congenita (SED), diastrophic dysplasia, pseudoachondroplasia, hypochondroplasia, and osteogenesis imperfecta (OI).

The most common forms of dwarfism are the following:


Of the estimated 200 types of dwarfism, achondroplasia is by far the most common. Achondroplastic dwarfism is characterized by an average-sized trunk, short arms and legs, and a slightly enlarged head and prominent forehead. Most achondroplastic dwarfs are born to average-sized parents, and account for somewhere between one in 26,000 and one in 40,000 births. Adults, on average, are four feet tall. Young children, especially, should be examined for such potential problems as central apnea, obstructive apnea, and hydrocephalus.

Diastrophic dysplasia

A relatively common form of dwarfism (about one in 100,000 births) first differentiated in 1960; before that, diastrophic dysplasia was thought to be a different form of achondroplasia. The condition is often characterized by short-limbed dwarfism and, in some cases, cleft palate, clubfeet, hitchhiker's thumb, and ears with a cauliflower appearance. Respiratory problems are sometimes present in infancy, but lifespan is normal. Serious orthopedic problems often require numerous surgical procedures.

Growth-hormone deficiency

Children with growth-hormone deficiency often grow normally until they are two or three years old, then fall behind their peers. Growth-hormone deficiency affects an estimated 10,000 to 15,000 people in the United States. Difficult to diagnose, it can be treated with regular injections of human growth hormone. Unlike skeletal dysplasias such as achondroplasia, diastrophic dysplasia, and SED, growth-hormone deficiency causes a short-stature condition in which a person's head, trunk, and limbs are in the same proportion as an average person. A person with this appearance used to be known as a "midget," although that term is now considered offensive.

Osteogenesis imperfecta (OI)

Between 20,000 and 50,000 Americans live with this genetic condition, which is characterized by brittle bones. There are four types of OI. Type III is a dwarfism condition, with adults generally reaching a height of three feet, although profound short stature is often associated with the other three types as well. Hearing loss is common among adults.


As the name implies, pseudoachondroplasia, like hypochondroplasia, was once thought to be closely related to achondroplasia. However, geneticists have since learned otherwise. In appearance, pseudoachondroplastic dwarfs share the same height as those with achondroplasia, but their head size is the same as that of average-size people, and they lack the facial features characteristic of achondroplasia. Children often are not diagnosed until they are two to three years old. Pseudoachondroplasia is associated with osteoarthritis and other orthopedic problems.

Spondyloepiphyseal dysplasia congenita (SED)

More commonly known as SEDc, or simply as SED, this genetic condition results in short stature, with adult height usually varying from slightly under three feet to slightly over four feet, although some adults are much taller. Other characteristics can include clubfeet, a cleft palate, and a barrel-chested appearance. SED is associated with a variety of medical problems, mainly orthopedic. SED occurs approximately once in every 100,000 births, making it, along with achondroplasia and diastrophic dysplasia, one of the most common forms of dwarfism.

Other related terms:

Double-Dominant Syndrome

A person with achondroplasia has one dwarfism gene and one average-size gene. If both parents have achondroplasia, there is a 25 percent chance their child will inherit the non-dwarfism gene from each parent and thus be average-size. There's a 50 percent chance the child will inherit one dwarfism gene and one non-dwarfism gene and thus have achondroplasia, just like her or his parents. And there is a 25 percent chance the child will inherit both dwarfism genes, a condition known a double-dominant syndrome, which invariably ends in death at birth or shortly thereafter.


In some circles, a "midget" is the term used for a proportionate dwarf. However, the term has fallen into disfavor and is considered offensive by most people of short stature. The term dates back to the 1860's, the height of the freak show era, and was generally applied only to short-statured persons who were displayed for public amusement, which is why it is considered so unacceptable today.

Such terms as "dwarf," "little person," "LP," and "person of short stature" are all acceptable, but most people would rather be referred to by their name than by a label.

Next: Find out more about the etymology of the words "dwarf" and "midget". »

The information above was excerpted and adapted from the Little People of America website with their permission. Copyright © 2005 by Little People of America, Inc. All rights reserved.