Description
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.
All people with hypochondroplasia have short stature. The adult height for men with this condition ranges from 138 centimeters to 165 centimeters (4 feet, 6 inches to 5 feet, 5 inches). The height range for adult women is 128 centimeters to 151 centimeters (4 feet, 2 inches to 4 feet, 11 inches).
People with hypochondroplasia have short arms and legs and broad, short hands
and feet
. Other characteristic features include a a large head (macrocephaly)
, limited range of motion at the elbows, a sway of the lower back (lordosis
), and bowed legs. These signs are generally less pronounced than those seen in people with achondroplasia and may not be noticeable until early or middle childhood. Affected individuals have a small increased risk of a seizure disorder known as temporal lobe epilepsy. Some studies have reported that a small percentage of people with hypochondroplasia have mild to moderate intellectual disability or learning problems, but other studies have produced conflicting results.
Frequency
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.
Causes
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.
Some people with hypochondroplasia do no have a variant in the FGFR3 gene. Researchers suspect that variants in other genes cause hypochondroplasia in these people, although these genes have not been identified.
Inheritance
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.
Other Names for This Condition
- HCH
- Hypochondrodysplasia
Additional Information & Resources
Genetic Testing Information
Genetic and Rare Diseases Information Center
Patient Support and Advocacy Resources
Clinical Trials
Catalog of Genes and Diseases from OMIM
Scientific Articles on PubMed
References
- Bober MB, Bellus GA, Nikkel SM, Tiller GE. Hypochondroplasia. 1999 Jul 15 [updated 2020 May 7]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from http://www.ncbi.nlm.nih.gov/books/NBK1477/ Citation on PubMed
- Cohen MM Jr. Some chondrodysplasias with short limbs: molecular perspectives. Am J Med Genet. 2002 Oct 15;112(3):304-13. doi: 10.1002/ajmg.10780. Citation on PubMed
- Foldynova-Trantirkova S, Wilcox WR, Krejci P. Sixteen years and counting: the current understanding of fibroblast growth factor receptor 3 (FGFR3) signaling in skeletal dysplasias. Hum Mutat. 2012 Jan;33(1):29-41. doi: 10.1002/humu.21636. Epub 2011 Nov 16. Citation on PubMed or Free article on PubMed Central
- Horton WA, Lunstrum GP. Fibroblast growth factor receptor 3 mutations in achondroplasia and related forms of dwarfism. Rev Endocr Metab Disord. 2002 Dec;3(4):381-5. doi: 10.1023/a:1020914026829. No abstract available. Citation on PubMed
- Vajo Z, Francomano CA, Wilkin DJ. The molecular and genetic basis of fibroblast growth factor receptor 3 disorders: the achondroplasia family of skeletal dysplasias, Muenke craniosynostosis, and Crouzon syndrome with acanthosis nigricans. Endocr Rev. 2000 Feb;21(1):23-39. doi: 10.1210/edrv.21.1.0387. Citation on PubMed
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