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Last updated May 14, 2018

Approved by: Maulik P. Purohit MD, MPH

Hypochondroplasia is a genetic disorder that affects bone growth and development.

What are the other Names for this Condition? (Also known as/Synonyms)

  • Achondroplasia Tarda
  • HCH
  • Hypochondrodysplasia

What is Hypochondroplasia? (Definition/Background Information)

  • Hypochondroplasia is a genetic disorder that affects bone growth and development. Individuals with Hypochondroplasia have a short stature (dwarfism). They also often have disproportionately short limbs when compared to the rest of their body
  • It is caused by a mutation in the FGFR3 gene in about 70% of the cases. The cause of Hypochondroplasia is unknown in the remaining 30%, though genetic mutations are implicated
  • The complications of Hypochondroplasia may include delayed intellectual growth, sleep apnea, severe spinal cord defects, and other bone abnormalities
  • There is no cure for Hypochondroplasia. The affected individuals may need lifelong treatment that may involve the use of growth hormones, limb lengthening and other surgical procedures, with appropriate management of the complications that may arise
  • The prognosis for Hypochondroplasia is generally good and many individuals are able to lead a normal quality of life

Who gets Hypochondroplasia? (Age and Sex Distribution)

  • Hypochondroplasia is a congenital disorder that is present at birth; symptoms of the disorder will exist throughout one’s life
  • Females are affected slightly more than males, though it is observed in both genders
  • The incident rate of Hypochondroplasia is anywhere between 1 in 15,000-40,000
  • Hypochondroplasia is prevalent around the world and all racial and ethnic groups are vulnerable to it

What are the Risk Factors for Hypochondroplasia? (Predisposing Factors)

  • Currently, a positive family history of Hypochondroplasia is the only known risk factor for the condition

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Hypochondroplasia? (Etiology)

  • Hypochondroplasia is a genetic disorder that is inherited in an autosomal dominant pattern (when there is a family history of the condition)
  • However, in most cases, Hypochondroplasia develops due to new mutation in the FGFR3 gene (when there is no positive family history of the condition). Nevertheless, the disorder can be passed on to the offspring (as an autosomal dominant trait) from one or both parents having the disorder, in subsequent generations
  • The normal function of the protein coded by the FGFR3 gene is to regulate bone and cartilage growth. A normal cartilage is required for proper bone growth. When FGFR3 gene is mutated, it results in increased inhibition of cartilage growth, which ultimately results in suppressed skeletal growth
  • It has been observed by researchers that not all cases of Hypochondroplasia occurs due to changes in the FGFR3 gene; other genetic mutations may be also involved (in as many 30% of the cases)

Autosomal dominant: Autosomal dominant conditions are traits or disorders that are present when only one copy of the mutation is inherited on a non-sex chromosome. In these types of conditions, the individual has one normal copy and one mutant copy of the gene. The abnormal gene dominates, masking the effects of the correctly function gene. If an individual has an autosomal dominant condition, the chance of passing the abnormal gene on to their offspring is 50%. Children, who do not inherit the abnormal gene, will not develop the condition or pass it on to their offspring.

What are the Signs and Symptoms of Hypochondroplasia?

Hypochondroplasia usually begins to manifest at birth and the signs and symptoms may include the following:

  • Short-statured individuals:
    • Males grow to an average height of 59 inches (152 cm)
    • Females grow to an average height of 55 inches (140 cm)
  • Short limbs, especially the upper limbs; short fingers and toes; broad hands
  • Large head
  • Bowed legs
  • Decreased muscle tone
  • Loose joints, limited motion range of the joints

Some features may be visible only after the baby completes his/her childhood development phase.

How is Hypochondroplasia Diagnosed?

Hypochondroplasia may be diagnosed using the following tools:

  • Complete physical examination with evaluation of comprehensive medical history
  • Radiographic studies for skeletal survey; especially of the skull, pelvis, and vertebral abnormalities
  • CT, MRI scan to assess spinal cord defects
  • Genetic tests and DNA analysis to detect any abnormal mutation
  • Prenatal exams include amniocentesis and chorionic villus sampling
  • A differential diagnosis may be undertaken to rule out other skeletal disorders

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Hypochondroplasia?

Complications due to Hypochondroplasia are usually mild or moderate. Severe cases are generally unusual and the complications that might arise include:

  • Bone and muscle anomalies that require surgical correction, such as bowlegs, inversion of the feet, joint pain causing serious discomfort, spinal cord narrowing (in rare cases), etc.
  • Mental growth delay
  • Learning disabilities
  • Sleep apnea: Spontaneous breathing stoppage while sleeping, due to obstruction in the throat (like tonsillitis), or due to obesity
  • Neurological abnormalities that include spinal cord compression and nerve dysfunction causing weakening of the legs
  • Infection of the middle ear

How is Hypochondroplasia Treated?

Hypochondroplasia is an incurable condition. An individualized treatment (case-by-case) approach is undertaken to improve the quality of life, based on the specific conditions/complications that develop in the individuals. These measures may include:

  • Orthopedic surgery to correct skeletal defects; limb-lengthening surgery to increase height (only if required by the individual)
  • Physical therapy
  • Growth hormone therapy

How can Hypochondroplasia be Prevented?

  • Most cases of Hypochondroplasia are related to genetic factors that are inherited; it cannot be prevented
  • Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
  • If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
  • Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders such as Hypochondroplasia
  • Regular medical screening at periodic intervals with tests, scans, and physical examinations are mandatory

What is the Prognosis of Hypochondroplasia? (Outcomes/Resolutions)

  • Most individuals with Hypochondroplasia can generally lead a good and full life with minimal medical complications. They may not be constrained in their choice of career selection and personal relations
  • Only those individuals with impaired mental growth and neurological signs and symptoms require medical attention and support for a longer period

Additional and Relevant Useful Information for Hypochondroplasia:

Societal acceptance and encouragement by families and friends play a vital supportive role in helping those with the disorder.

What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

Helpful Peer-Reviewed Medical Articles:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Nov. 12, 2015
Last updated: May 14, 2018