Rare Classroom: Achondroplasia

Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The disease that we will be learning about today is:


What is Achondroplasia?

  • Achondroplasia is a genetic disorder whose primary characteristic is dwarfism.
    • In popular culture, achondroplasia is often called dwarfism, but while it is the most common cause of dwarfism, there are other disorders that cause dwarfism as well.
  • People with the condition have shortened arms and legs, with a torso that is of normal size. The head and forehead may also be enlarged
  • Incidence is around 1 in 27,500 people
  • Diagnosis is typically based on signs and symptoms, but can also include genetic testing

How Do You Get It?

  • A principal risk factor for the disorder is the age of the father. A child with an older father is at greater risk
    • This is partially due to aging, but also due to increased exposure to ionizing radiation
  • Achondroplasia is caused by a mutation impacting a gene called FGFR3
    • This mutation is inherited in an autosomal dominant fashion
    • This mutation originates in the father’s sperm
  • 80 percent of cases are the result of a new mutation; the remainder are inherited
  • If two copies of the gene are inherited (one from both parents), the condition is fatal before or soon after birth.

What Are The Symptoms?

  • The classic signs and symptoms of achondroplasia are:
    • Shortened arms and legs
    • Enlarged head and forehead
  • Other symptoms include:
    • Shortened fingers and toes
    • Abnormally high rate of ear infections
      • This is usually due to blockage of the Eustachian tube, which links the nasopharynx to the middle ear
    • ‘Knock knee’, or ‘bowlegged’ deformities
    • Small mid-face
    • Flattened nasal bridge
    • Spinal curvature
  • In childhood, delays in motor and walking development are common
  • More serious complications include:
    • Hydrocephalus
    • Spinal stenosis
    • Obstructive sleep apnea
    • Obesity
  • Average height for affected males is 4 ft 4 in; for females, 4 ft

How Is It Treated?

  • No cure has been developed for achondroplasia
  • However, a number of treatments have been developed, particularly for the most threatening complications
  • Human growth hormone (HGH) doesn’t help achondroplasia in the long term, but can increase growth for a year or two
  • A drug in development called vosoritide has been effective in clinical trials
  • Complications are treated with preventative measures, or as they appear
  • Life expectancy for achondroplasia patients is around ten years less than unaffected people on average
  • Finding community support groups can also be a valuable component of improving quality of life

Where Can I Learn More???

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