Hypochondroplasia

Hypochondroplasia is a developmental disorder caused by an autosomal dominant genetic defect in the fibroblast growth factor receptor 3 gene (FGFR3) that results in a disproportionately short stature, micromelia, and a head that appears large when compared with the underdeveloped portions of the body. It is also known as "achondroplasia tarda" and "atypical achondroplasia."

It is classified as short-limbed dwarfism.

Features
People affected by this disorder appear normal at birth. As the infant grows, however, their arms and legs do not develop properly and their body becomes thicker and shorter than normal. The head is normal but appears large due to the underdevelopment of other parts of the body, a symptom called "relative macrocephaly".

The clinical and radiographic features of this disorder are milder than those seen in achondroplasia.

Intelligence is usually normal.

Pathophysiology
This disorder results from mutations in the proximal tyrosine kinase domain of the FGFR3 gene. This gene plays an important role in embryonic development, playing a part in regulating activities such as cell division, migration, and differentiation.

Getting Help
Standard treatment of hypochondroplasia usually takes the form of orthopedic surgery and physical therapy. Genetic counseling is advised for patients and their families.

Etiology
This disorder is transmitted as an autosomal dominant trait affecting the FGFR3 gene on chromosome 4p16.3. There is no cure for this condition.

Epidemiology
Females tend to be affected more often than males.