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Achondroplasia - Symptoms and Treatment


Achondroplasia is a type of autosomal dominant genetic disorder that is a common cause of dwarfism . People with this condition have short stature , usually reaching a full adult height of around 4 feet or 1.2 meters . The average height of an adult with achondroplasia is 131 cm (52 inches, or 4 foot 4) in males and 124 cm (49 inches, or 4 foot 1) in females. Achondroplasia is the most common cause of short stature with disproportionately short limbs. There is a typically large head with prominence of the forehead (frontalb ossing), underdevelopment (hypoplasia) of the midface with cheekbones that lack prominence, and a low nasal bridge with narrow nasal passages. The brain is normal and intelligence is entirely normal in achondroplasia. However, the complications of achondroplasia can impinge on the brain and the spinal cord. Achondroplasia is one of the oldest known birth defects. The frequency of achondroplasia is estimated to range from about 1 in 10,000 births in Latin America to about 12 in 77,000 in Denmark. An average figure worldwide is approximately 1 in 25,000 births.

Achondroplasia is a disorder of bone growth. It is the most common of a group of growth defects characterized by abnormal body proportions. Affected individuals have arms and legs that are very short, while the torso is nearly normal size. The characteristic facial features include a prominent forehead and a flattened bridge of the nose. Although this condition can be inherited in an autosomal dominant manner, 80% of cases are due to new, sporadic mutations. Mutations involve the gene encoding fibroblast growth factor receptor 3 (FGFR3), situated on chromosome 4. Most commonly, a point mutation causes the substitution of arginine for glycine (G380R) in the transmembrane region of the receptor. There is growing evidence that mutations of FGF3R confer a "gain of function". It is proposed that the normal function of FGFR3 is to slow down the formation of bone by inhibiting the proliferation of chondrocytes, the cells that produce cartilage. The mutation increases the activity of FGFR3, severely limiting bone growth. This theory is supported by the knock-out mouse model in which the receptor is absent, and so the negative regulation of bone formation is lost. The result is a mouse with excessively long bones and elongated vertebrae, resulting in a long tail. Achondroplastic mouse models are useful tools in developing potential treatments.

Causes of Achondroplasia

The common Causes of Achondroplasia :

  • Children of normal-sized parents who carry a mutated FGFR3 gene.
  • Advanced paternal age causing spontaneous mutations.
  • Children of a parent with achondroplasia.

Symptoms of Achondroplasia

Some common Symptoms of Achondroplasia :

  • Short stature.
  • Hypotonia.
  • Skeletal (limb) abnormalities.
  • Short limbs (upper arm and thigh).
  • Polyhydramnios.
  • Waddling gait.
  • Spinal stenosis.
  • Bowed legs.

Treatment of Achondroplasia

  • Surgery is sometimes needed to correct specific skeletal deformities.
  • In children with signs of craniomedullary compression, surgical treatment to release the compression can improve neurologic, cognitive, and respiratory functions.
  • Pregnant women with achondroplasia should have their babies delivered by cesarean birth.
  • Surgical decompression of the cord is needed to relieve the pressure on it. This is done by opening the canal at the affected levels in a procedure called a "laminectomy."
  • Knowledgeable pediatric care and periodic orthopedic and neurologic examinations are critical.
  • Related abnormalities, including spinal stenosis and spinal cord compression, should be treated when they cause problems.

 

 


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