Achondroplasia and Hypochondroplasia: Dwarfism

Is a genetic autosomal dominate (de novo mutation) genetic disorder of the long bones. Rhizomelic (proximal) shortening in the upper part of the arms and legs.

A newborn with Hypochondroplasia will be average length and weight.

Parent’s with a child with Hypochondroplasia are usually the result of a spontaneous gene mutation on the FGFR3 gene. Unless a parents has the affected gene, parents would not have any additional risk of producing another child with Hypochondroplasia, than the first time. If a parent carries the mutated FGFR3 gene, then they have a 50-50 percent chance of passing it on. If both parent carry the affected gene, then they have a 25% chance of having an average height child, a 25% chance of having double dominate child and a 50% chance of having a child with Hypochondroplasia.

In 1995, scientists found the cause of Achondroplasia and Hypochondroplasia. The FGFR3 gene or fibroblast growth factor receptor 3 is (believed) responsible for the limited regulation of bone growth in both Achondroplasia and Hypocondroplasia.

We have talked a lot about Achondroplasia, but there is another form of dwarfism, similar to Achondroplasia called Hypochondroplasia.

Hypochondroplasia is a milder form of Achondroplasia. In Hypochondroplasia, the head is large as it is with Achondroplasia, with less frontal bossing. The limbs present longer than Achondroplasia and there will be less features of the trident fingers. There will also be fewer medical complications with Hypochondroplastic dwarfs.

Comparing the two, a Hypochondroplastic dwarf will be taller and present less prominent features than those with Achondroplasia. Individuals with Hypo can reach an adult height of 4 feet 6 inches to 5 feet 5 inches.

A child with Hypochondroplasia is typically diagnosed at a later age because their growth tends to slow down and if their features are very mild, they may not be diagnosed until adulthood.

Hypochondroplasia:

Hypochondroplasia is a skeletal dysplasia characterized by short stature; stocky build; disproportionately short arms and legs; broad, short hands and feet; mild joint laxity; and macrocephaly. Radiologic features include shortening of long bones with mild metaphyseal flare; narrowing of the inferior lumbar itnerpedicular distances; short, broad femoral neck; and squared, shortened ilia. The skeletal features are very similar to achondroplasia but usually tend to be milder. Medical complications common to achondroplasia (e.g., spinal stenosis, tibial bowing, obstructive apnea) occur less frequently in hypochondroplasia but deficits in mental capacity and/or function may be more prevalent. Children usually present as toddlers or school-age children with failure to grow; with age, limb disproportion and other features become more prominent.

It is believed that some Hypochondroplastic dwarfs may have some mild to moderate mental retardation or slow cognitive deficits.

It is recommended that any testing common with Achondroplasia, also be followed for individuals with Hypochondroplasia.

*Measurement of height, weight, and head circumference and plotting on achondroplasia-standardized growth curves
*Neurologic examination for signs of spinal cord compression, with referral to a pediatric neurologist if needed
*Screening developmental assessment
*MRI or CT examination of the foramen magnum if findings suggest severe hypotonia or spinal cord compression
*History for evidence of sleep apnea, with formal sleep study if suggestive
*Evaluation for thoracic or lumbar gibbus in the presence of truncal weakness
*Examination for leg bowing, with orthopedic referral if bowing interferes with walking
*Speech evaluation at diagnosis or by age two years

Since the two dysplasia’s are easily confused, there is no such thing as “Mild Achondroplasia” or “A form of Achondroplasia”. You either have it or don’t.

*Edited to add: That some individuals with Hypochondroplasia as with individuals with Achondroplasia may not show a gene change when tested through blood work. When this happens, skeletal X-rays are relied upon to make a diagnosis. Even then, doctor’s are still uncertain until the child grows and continues to fall of the growth chart.

There are several families with child who have Hypochondroplasia and you may find their blogs here:

Andrea is mom to four beautiful children, one who has Hypochonroplasia

http://keepingupwiththekunzs.blogspot.com/

Sonya is mom to three All American boys. She is married to John who was recently diagnosed with Hypochondroplasia as was one of her sons.

http://jadenworld-jadensworld.blogspot.com/

If you have a blog about raising a child with Hypochondroplasia and would like to be included in my blog roll, please contact me here.

*This information can be found here.