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."
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.
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.
^ Santos HG, Almeida M, Fernandes H, Wilkie A (2007). "Clinical hypochondroplasia in a family caused by a heterozygous double mutation in FGFR3 encoding GLY380LYS". Am. J. Med. Genet. A143 (4): 355–9. doi:10.1002/ajmg.a.31556. PMID 17256796.
^ Rousseau F, Bonaventure J, Legeai-Mallet L, et al (1996). "Clinical and genetic heterogeneity of hypochondroplasia". J. Med. Genet.33 (9): 749–52. PMID 8880574.
^ Heuertz S, Le Merrer M, Zabel B, et al (2006). "Novel FGFR3 mutations creating cysteine residues in the extracellular domain of the receptor cause achondroplasia or severe forms of hypochondroplasia". Eur. J. Hum. Genet.14 (12): 1240–7. doi:10.1038/sj.ejhg.5201700. PMID 16912704.