Achondroplasia

(Achondroplastic Dwarfism)

Definition

Achondroplasia is a genetic disorder that causes short stature called dwarfism and a large head, also known as macrocephaly. It is a disorder in which bone and cartilage do not grow normally. It is the most common cause of dwarfism.This condition leads to people reaching a full-grown height of less than four feet. The greatest shortening occurs in the bone between the shoulder and the elbow and the bone between the hip and the knee. There may also be underdevelopment of the face.

Causes

Achondroplasia is a genetic disorder. It is caused by mutations in the FGFR3 gene. This gene prevents the growth of cartilage at the growth plate. FGFR3 encodes a protein called Fibroblast Growth Factor Receptor 3. This protein is the site of action of a major growth factor responsible for lengthening bones. When this growth factor cannot act properly due to the absence of its receptor, the growth of bones, at the growth plate's cartilage, is slowed. This leads to shorter bones, abnormally shaped bones, and shorter stature.The gene for achondroplasia can be passed from one generation to the next. If a parent has the disorder, there is a 50% chance of passing the gene for achondroplasia to children. In most cases of achondroplasia, it more commonly is the result of a sudden genetic defect that occurs in the developing embryo.

Risk Factors

Factors that may increase the chance of achondroplasia include:
  • Children of a parent with achondroplasia
  • Children of normal-sized parents who carry a mutated FGFR3 gene
  • Advanced paternal age causing spontaneous mutations

Symptoms

Symptoms of achondroplasia include:
  • Short stature, a long trunk, and shortened limbs, which are noticeable at birth
  • An adult height of between 42-56 inches
  • A head that is large and a forehead that is prominent
  • Portions of the face can be underdeveloped
  • At birth, the legs appear straight, but as a child begins to walk, he or she develops a knock-knee or bowed-leg deformity
  • The hands and the feet appear large, but the fingers and toes are short and stubby
  • Straightening of the arm at the elbow may be limited, but usually does not keep someone from doing any specific activities
  • Children may develop an excessive curve of the lower back and a waddling walking pattern
  • Dental problems
Other common symptoms include:
  • Weight control problems
  • Dental problems from overcrowding of teeth
  • Neurologic and respiratory problems
  • Fatigue, pain, and numbness in the:
    • Lower back
    • Spine

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