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It is possible that the main title of the report Achondroplasia is not the name you expected.

Disorder Subdivisions

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General Discussion

Achondroplasia is a rare genetic disorder characterized by an unusually large head (macrocephaly) with a prominent forehead (frontal bossing) and flat (depressed) nasal bridge; short upper arms and legs (rhizomelic dwarfism), unusually prominent abdomen and buttocks; and short hands with fingers that assume a "trident" or three-pronged position during extension. An autosomal dominant genetic trait, achondroplasia occurs as a result of a fresh (new) spontaneous change (mutation) in genetic material in about 90 percent of cases. In achondroplasia, affected individuals have impaired ability to form bone from cartilage (endochondral bone formation).


Achondroplasia is a rare genetic disorder characterized by an unusually large head (macrocephaly) with a prominent forehead (frontal bossing) and flat (depressed) nasal bridge, short upper arms and legs (rhizomelic dwarfism), unusually prominent abdomen and buttocks, and short hands with fingers that assume a "trident" or three-pronged position during extension.

Infants born with achondroplasia typically have an arched or "dome-like" (vaulted) skull to adapt to the abnormally enlarged brain (megalencephaly) that is characteristic in this syndrome. This results in a very broad forehead. Excessive accumulation of fluid around the brain (hydrocephalus) may also be present. Compression of the brain stem may occur in some children with achondroplasia resulting in a life-threatening condition. (For more information on this disorder, choose "Hydrocephalus" as your search term in the Rare Disease Database.)

Infants with achondroplasia typically have a flat (depressed) nasal bridge. Arms and legs are usually very short and the trunk of the body appears long in comparison. The hands of children with this disorder are generally short and broad. The index and middle finger are typically close together as are the ring finger and the pinkie, giving the hand a three pronged (trident) appearance. An abnormal condition of the spine characterized by the outward (convex) curvature of the upper back (dorsal kyphosis) is usually present in children with this disorder and their legs may be bowed. Most adult males with Achondroplasia are under, 4 feet 6 inches tall, while females are typically 3 inches shorter than males.

Children with achondroplasia may also have deformities of the rib cage including the excessive curvature or "cupping" of the ribs. Achondroplasia does not cause any impairment or deficiencies in mental abilities. The life expectancy of infants over the age of 12 months is normal.


In most cases, achondroplasia appears to occur randomly for unknown reasons (sporadically) with no apparent family history. According to researchers, many such cases may represent new (sporadic) genetic changes (mutations) that may be transmitted as an autosomal dominant trait (i.e., new dominant gene mutations). Investigators indicate that increased age of the father (advanced paternal age) may be a contributing factor in cases of sporadic achondroplasia.

Less commonly, familial cases of achondroplasia have been reported. In such instances, autosomal dominant inheritance has been demonstrated. Human traits, including the classic genetic diseases, are the product of the interaction of two genes, one received from the father and one from the mother. In dominant disorders, a single copy of the disease gene (received from either the mother or father) may be expressed "dominating" the other normal gene and resulting in the appearance of the disease. The risk of transmitting the disorder from affected parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child. The risk is the same for each pregnancy.

Achondroplasia has been shown to result from specific mutations of a gene known as "fibroblast growth factor receptor-3" (FGFR3). The FGFR3 gene is located on the short arm (p) of chromosome 4 (4p16.3). Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as "p" and a long arm identified by the letter "q." Chromosomes are further subdivided into bands that are numbered. Therefore, chromosome 4p16.3 refers to band 16.3 on the short arm of chromosome 4.

Genetic analysis has also revealed that different mutations of the same gene (i.e., FGFR3) may cause a disorder known as hypochondroplasia, indicating that achondroplasia and hypochondroplasia are allelic disorders. (An allele is one of two or more alternative forms of a gene that may occupy a particular chromosomal location.) Hypochondroplasia is a form of short-limbed dwarfism that may be characterized by certain features similar to those seen in achondroplasia. (For more information, please see the "Related Disorders" section of this report below.)

Affected Populations

Achondroplasia appears to affect males and females in relatively equal numbers. This disorder begins in the developing fetus and is one of the most common forms of skeletal dysplasia that causes dwarfism. The estimated frequency of achondroplasia has ranged from about one in 15,000 to one in 35,000 births.

Standard Therapies

Ultrasonography or magnetic resonance imaging (MRI) of the brain in infancy may be done to determine the presence of hydrocephalus which is sometimes associated with achondroplasia. Orthopedic surgery and physical therapy may be beneficial in the management of this disorder. Genetic counseling may also be useful.

Little People of America is an organization providing social services for persons with achondroplasia. The organization also acts as an advocate on their behalf (see Resources Section of this report).

The Vertical Expandable Prosthetic Titanium Rib (VEPTR) was approved by the FDA in 2004 as a treatment for thoracic insufficiency syndrome (TIS) in pediatric patients. TIS, is a congenital condition where severe deformities of the chest, spine, and ribs prevent normal breathing and lung development. The VEPTR is an implanted, expandable device that helps straighten the spine and separate ribs so that the lungs can grow and fill with enough air to breathe. The length of the device can be adjusted as the patient grows. The titanium rib was developed at the University of Texas, Health Science Center in San Antonio. It is manufactured by Synthes Spine Co.. //

For more information, please contact:

Synthes, Inc.

1302 Wrights Lane East

West Chester, PA 19380


Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010


For information about clinical trials sponsored by private sources, contact:

Two clinical trials associated with the Human Genome Project have been completed. One studied the genes responsible for skeletal disorders and short statue. The other study explored issues surrounding prenatal genetic testing for achondroplasia.



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Stoilov I, et al. A common FGFR3 gene mutation is present in achondroplasia but not in hypochondroplasia. Am J Med Genet. 1995;55:127-33.

Bellus GA, McIntosh I, Smith EA, et al. A recurrent mutation in the tyrosine kinase domain of fibroblast growth factor receptor 3 causes hypochondroplasia. Nat Genet. 1995;10:357-59.

Shiang R, Thompson LM, Zhu YZ, et al. Mutations in the transmembrane domain of FGFR3 cause the most common genetic form of dwarfism, achondroplasia. Cell. 1994;78:335-42.

Rousseau F, Bonaventure J, Legeai-Mallet L, et al. Mutations in the gene encoding fibroblast growth factor receptor-3 in achondroplasia. Nature. 1994;371:252-54.

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Le Merrer M, Rousseau F, Legeai-Mallet L, et al. A gene for achondroplasia -hypochondroplasia maps to chromosome 4p. Nature Genet. 1994;6:314-17.

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Stoll C, Roth MP, Bigel P. A reexamination of parental age effect on the occurrence of new mutations for achondroplasia. In: Papadatos CJ, et al., eds. Skeletal Dysplasias. New York, NY: Alan R. Liss; 1982:419-26.


Online Mendelian Inheritance in Man, OMIM (TM). John Hopkins University, Baltimore, MD. MIM Number 100800; 2/6/01. Available at: //

Online Mendelian Inheritance in Man, OMIM (TM). John Hopkins University, Baltimore, MD. MIM Number 146000; 1/11/01. Available at: //


Supporting Organizations

European Skeletal Dysplasia Network

Institute of Genetic Medicine
Newcastle University
Newcastle upon Tyne, NE1 3BZ
United Kingdom
Tel: 441612755642
Fax: 441612755082
Website: //

Genetic and Rare Diseases (GARD) Information Center

PO Box 8126
Gaithersburg, MD 20898-8126
Tel: (301)251-4925
Fax: (301)251-4911
Tel: (888)205-2311
Website: //

Human Growth Foundation

997 Glen Cove Avenue
Suite 5
Glen Head, NY 11545
Tel: (516)671-4041
Fax: (516)671-4055
Tel: (800)451-6434
Website: //

Little People of America, Inc.

250 El Camino Real Suite 201
Tustin, CA 92780
Tel: (714)368-3689
Fax: (714)368-3367
Tel: (888)572-2001
Website: //

MAGIC Foundation

6645 W. North Avenue
Oak Park, IL 60302
Tel: (708)383-0808
Fax: (708)383-0899
Tel: (800)362-4423
Website: //

March of Dimes

1275 Mamaroneck Avenue
White Plains, NY 10605
Tel: (914)997-4488
Fax: (914)997-4763
Email: or
Website: // and

NIH/National Institute of Arthritis and Musculoskeletal and Skin Diseases

Information Clearinghouse
One AMS Circle
Bethesda, MD 20892-3675
Tel: (301)495-4484
Fax: (301)718-6366
Tel: (877)226-4267
Website: //

Restricted Growth Association

PO Box 5137
Yeovil, BA20 9FF
United Kingdom
Tel: 3001111970
Fax: 3001112454
Website: //

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see