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ABCMD definition of Achondroplasia: A disease causing abnormal development of bones resulting in shortening and dwarfism.

Basics of Achondroplasia

Achondroplasia is one of many diseases that can result in dwarfism.  Dwarfism is caused by abnormal bone growth and development. With Achondroplasia the resulting dwarfism is disproportionate. This means in Achondroplasia, the arms and legs are shortened more then the trunk.  Some diseases can actually lead to proportionate dwarfism.  With these diseases, such as in mucopolysaccharidoses, there is equal shortening of the arms and legs along with the trunk. 

Achondroplasia is an autosomal dominant condition (AD). This means an abnormal gene causing this disease could have come from either mom or dad.  

What causes Achondroplasia

Achondroplasia is most commonly caused by a defect in a growth receptor within bones called Fibroblast growth factor receptor 3 (FGFR3).  80% of individuals with Achondroplasia have this as the cause of their disease.  The problem with this growth factor receptor  leads to problems with the growth plates within bones called the physis. Specifically the problem lies within the proliferative zone of the physis. 

Normally Fibroblast growth factor travels within your blood to the growth plate in your bones and tells it to grow by binding to (forming a connection with) the growth factor receptor on the cells in your bones.  In Achondroplasia, the receptors that normally bind the growth factors are not working properly causing less growth then usual. Some normal growth still occurs, however not levels found in patients without this disease.  Achondroplasia, in simple terms, is a quantitative issue with bone growth (not enough) and not a qualitative issue.  This, as you may understand, causes bones to be shorter then usual and leads to dwarfism. 

What are the signs and symptoms of Achondroplasia

Patients with Achondroplasia typically have some of the following characteristics:

• Shortened arms and legs with a normal trunk (disproportionate dwarfism). As the trunk can be normal, children often have normal sitting heights compared to other children. However, when standing they are notably shorter; often less then the 3rd percentile for height for age. 
  
  
  
  • Often the part of the limb closest to the trunk is shortened the most in Achondroplasia. This is called Rhizomelic shortening. For example, with Rhizomelic shortening, the humerus (bone in your upper arm) would be shorter then the bones in your forearm. 
  
  
• Button noses
  
• Trident hands
  
• Spine disorders: such as thoracolumbar kyphosis or lumbar stenosis (narrowing of the space for the spinal cord in the lower back)  
  
• Children are often of normal intellegence, however may take longer to reach normal milestones with motor function.   
  
• Hypotonia
  
• Champpagne glass pelvis. As the bone developement and growth is abnormal, the pelivs is wider then it is deep. 
  
• Genu Varum (bow-legged)
  
• Coxa Valga (hips rotated abnormally)
  
• Etc.

How is Achondroplasia treated

Achondroplasia itselt does not truly require treatment.  Instead, many of the goals for "treatment" of Achondroplasia deal with allowing people to live normal and productive lives.  This may include altered housing, transportation, etc. 

True treatment for Achondroplasia is required for the problems that come with the disease.  Some of the most severe problems that come with Achondroplasia are problems with the spine.  Treatment for spine problems can include bracing or surgery. For example, patients with lumbar stenosis (narrowing of the space for the spinal cord in the lower back) often have decompressive surgery. With decompression, the bone surrounding the spinal cord closest to the back is removed to allow more space for the spinal cord and nerves. 

Patients with severe genu varum (bow-legged) deformities can have their bones cut and re-aligned. This is called an osteotomy.  Other options include hemiepiphyseodesis. This entails stopping growth in a chosen part of the growth plate with goals of changing the shape/alignment of the growing bone. 

Some patients undergo limb lengtheing procedures as well, however there is a high risk of complications/things going wrong with these procedures.  One form of bone lengtheing is called distraction osteogenesis.  With distraction osteogenesis a fracture (break in the bone) is made intentially in the patient's bone.  Your body responds to fractures by trying to repair the fracture and making more bone.  As your body works to heal the fracture, the bones are slowly pulled apart (distracted) over weeks to months by your doctor. Your body can fill the space between the 2 bones being pulled apart with new bone (osteogenesis), thus increasing length.  These procedures are controversial.