Achondroplasia (ACH) is a disorder of the genes. The changes in the genes causes short stature and a large head. It is the most common cause of dwarfism.
People with ACH reach a full-grown height of around 4-4½ feet. The arm bone between the shoulder and the elbow and the leg bone between the hip and the knee are most affected. It may also affect how the face develops.
ACH is caused by a change in the FGFR3 gene. This gene controls how bones and cartilage grow. A defect in the gene prevents normal growth and leads to shorter and abnormally shaped bones.
The defect can occur suddenly, for no known reason. It early in pregnancy when the sperm and egg meet. The gene can also be passed through a family, though this is less common. If a parent has the defective gene, there is a 50% chance the child will have it. You can carry the gene and not have ACH.
Factors that may increase the chance of ACH include:
Parent with ACH
Parents without who carry a mutated FGFR3 gene
Advanced age of father
Characteristics of ACH include:
Short stature, a normal trunk, and shortened limbs, which are noticeable at birth
An adult height around 4-4½ feet
A head that is large and large forehead
Some of face may be underdeveloped
Knees have inward or bow-legged appearance once child starts to walk
Fingers and toes are short and stubby
Arm may not be fully straight at elbow
May be an excessive curve of the lower back
Waddling walking pattern
Problems with mouth like overcrowding of teeth
Other common symptoms include:
Weight control problems
Problems of the nervous system
Fatigue, pain, and numbness in the:
ACH may be visible during prenatal testing. If the doctor suspects ACH, other tests may be recommended. An amniocentesis can remove a small amount of fluid from around the baby. Genetic testing can be done to confirm ACH.
After birth, the doctor will do a physical exam. Images of the bones may be taken with:
Aldegheri R, Dall'Oca C. Limb lengthening in short stature patients. J Pediatr Orthop B. 2001;10(3):238-247.
Aviezer D, Golembo M, Yayon A. Fibroblast growth factor receptor-3 as a therapeutic target for achondroplasia—genetic short limbed dwarfism. Curr Drug Targets. 2003;4(5):353-65.
Last reviewed March 2018 by
EBSCO Medical Review Board
James P. Cornell, MD
Last Updated: 12/11/2018
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