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Achondroplasia
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Achondroplasia

Achondroplasia is the most common form of short-limbed dwarfism, characterized by a difficulty in converting cartilage to bone. This genetic condition results in short stature, distinctive skeletal features, and potential complications such as spinal stenosis.

Overview

Achondroplasia is the most common form of short-limbed dwarfism. The word achondroplasia means "without cartilage formation." Cartilage is a tough but flexible tissue that makes up much of the skeleton during early development. However, in people with achondroplasia, the problem is not forming cartilage but converting it to bone (a process called ossification), particularly in the long bones of the arms and legs. Achondroplasia is similar to another skeletal disorder called hypochondroplasia, but the features of achondroplasia tend to be more severe.

Symptoms and Physical Features

All people with achondroplasia have short stature. Without treatment, the average height of an adult male with achondroplasia is 131 centimeters (4 feet, 4 inches), and the average height for adult females is 124 centimeters (4 feet, 1 inch).

Characteristic features and associated health problems include:

  • An average-size trunk with short arms and legs, particularly short upper arms and thighs.
  • Limited range of motion at the elbows.
  • An enlarged head (macrocephaly) with a prominent forehead (frontal bossing).
  • Short fingers, where the ring finger and middle finger may diverge, giving the hand a three-pronged (trident) appearance.
  • A pronounced and permanent sway of the lower back (lordosis) and bowed legs, which usually develop in childhood.
  • Abnormal front-to-back curvature of the spine (kyphosis) and back pain in some affected individuals.
  • Obesity and recurrent ear infections.
  • Normal intelligence.

Complications

As affected individuals age, they may experience potentially serious complications:

  • Spinal Stenosis: A narrowing of the spinal canal that can pinch (compress) the upper part of the spinal cord. This causes pain, tingling, and weakness in the legs that can make walking difficult.
  • Foramen Magnum Stenosis: An uncommon but serious complication in early childhood involving the narrowing of the hole at the base of the skull where the spinal cord exits the brain. This can cause compression of the brain stem, leading to pauses in breathing during sleep (sleep apnea) or hydrocephalus (a buildup of fluid in the brain that can lead to increased head size and related brain abnormalities).

Frequency

Achondroplasia occurs in 1 in 15,000 to 40,000 newborns.

Causes

Variants (also called mutations) in the FGFR3 gene cause achondroplasia. The FGFR3 gene provides instructions for making a protein involved in the development and maintenance of bone and brain tissue. Two specific variants in this gene are responsible for almost all cases of achondroplasia. These variants cause the FGFR3 protein to be overly active, which interferes with skeletal development and leads to the disturbances in bone growth seen with this disorder.

Associated Gene

  • FGFR3

Inheritance Pattern

Achondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

About 80 percent of people with achondroplasia are born to parents who do not have the condition and are of average height; these cases are caused by new mutations in the FGFR3 gene. In the remaining cases, individuals inherit an altered gene from one or two parents with achondroplasia.

Individuals who inherit two altered copies of the FGFR3 gene typically have a severe form of achondroplasia that causes extreme shortening of the bones and an underdeveloped rib cage. These individuals are usually stillborn or die shortly after birth from respiratory failure.

Other Names for This Condition

  • ACH
  • Achondroplastic dwarfism
  • Dwarf, achondroplastic

Frequently Asked Questions

Most cases of achondroplasia result from a new (de novo) mutation, meaning neither parent has the condition. However, if one parent has achondroplasia, there is a 50 percent chance of passing the gene to each child. If both parents have achondroplasia, there is a 25 percent chance the child will have homozygous achondroplasia, a severe and often fatal form of the condition, which is why genetic counseling is strongly recommended for couples where both partners are affected.
s people with achondroplasia age, the spinal canal can narrow, leading to spinal stenosis. Early warning signs include numbness or tingling in the legs, weakness in the lower limbs, difficulty walking, or changes in bladder and bowel control. These symptoms indicate compression of the spinal cord or nerve roots and require immediate medical evaluation to prevent permanent neurological damage.
Growth hormone therapy is generally not effective for achondroplasia because the underlying issue is a defect in cartilage-to-bone conversion, not a lack of growth hormone. Limb-lengthening surgery is an option but is complex, painful, and carries significant risks. It is typically reserved for adults who are highly motivated and have realistic expectations, as it does not change the proportion of the limbs to the trunk and requires extensive rehabilitation.
Individuals with achondroplasia are prone to recurrent ear infections (otitis media) and conductive hearing loss due to the structure of the middle ear and Eustachian tubes. This can impact speech development in children. Standard management includes regular hearing screenings, prompt treatment of ear infections, and the potential use of tympanostomy tubes (ear tubes) to drain fluid and improve hearing.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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