Hypochondroplasia is a form of short-limbed dwarfism. This condition affects the conversion of cartilage into bone (a process called ossification), particularly in the long bones of the arms and legs. Hypochondroplasia is similar to another skeletal disorder called achondroplasia, but the features tend to be milder.

The vast majority of cases of hypochondroplasia are caused by variants in the FGFR3 gene. This gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. Although it remains unclear how FGFR3 gene variants lead to the features of hypochondroplasia, researchers believe that these genetic changes cause the protein to be overly active. The overactive FGFR3 protein likely interferes with skeletal development and leads to the disturbances in bone growth that are characteristic of this disorder.

The incidence of hypochondroplasia is unknown. Researchers believe that it may be about as common as achondroplasia, which occurs in 1 in 15,000 to 40,000 newborns. More than 200 people worldwide have been diagnosed with hypochondroplasia.

Hypochondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Most people with hypochondroplasia are born to parents who do not have the condition and are of average heights; these cases are caused by new variants in the FGFR3 gene. In the remaining cases, people with hypochondroplasia inherit an altered FGFR3 gene from one or two affected parents.  Individuals who inherit two altered copies of this gene typically have more severe problems with bone growth than those who inherit a single FGFR3 variant.

Published Date: May 29, 2023
Published By: National Institutes of Health