|Jason "Wee Man" Acuña, an American actor and stunt performer with achondroplasia|
|Symptoms||Short arms and legs, enlarged head, prominent forehead|
|Complications||Ear infections, hyperlordosis, back pain, spinal stenosis, hydrocephalus|
|Causes||Genetic (autosomal dominant mutation in the FGFR3 gene)|
|Risk factors||Paternal age|
|Diagnostic method||Based on symptoms, genetic testing if uncertain|
|Differential diagnosis||Hypochondroplasia, thanatophoric dysplasia, cartilage-hair hypoplasia, pseudoachondroplasia|
|Treatment||Support groups, growth hormone therapy, treatment of complications|
|Frequency||1 in 27,500 people|
Achondroplasia is a genetic disorder whose primary feature is dwarfism. In those with the condition, the arms and legs are short, while the torso is typically of normal length. Those affected have an average adult height of 131 centimetres (4 ft 4 in) for males and 123 centimetres (4 ft) for females. Other features can include an enlarged head and prominent forehead. Complications can include sleep apnea or recurrent ear infections.
Achondroplasia is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene that results in its protein being overactive. The disorder has an autosomal dominant mode of inheritance, meaning only one mutated copy of the gene is required for the condition to occur. About 80% of cases result from a new mutation, which originates in the father's sperm. The rest are inherited from a parent with the condition. The risk of a new mutation increases with the age of the father. In families with two affected parents, children who inherit both affected genes typically die before birth or in early infancy from breathing difficulties. The condition is generally diagnosed based on the symptoms but may be confirmed by genetic testing.
Treatments may include support groups and growth hormone therapy. Efforts to treat or prevent complications such as obesity, hydrocephalus, obstructive sleep apnea, middle ear infections or spinal stenosis may be required. Achondroplasia is the most common cause of dwarfism and affects about 1 in 27,500 people.
Signs and symptoms
- Disproportionate dwarfism
- Shortening of the proximal limbs (called rhizomelic shortening)
- Short fingers and toes, with "trident hands" (short hands with stubby fingers, and a separation between the middle and ring fingers – reminiscent of a trident on fetal ultrasound )
- Large head with prominent forehead frontal bossing
- Small midface with a flattened nasal bridge
- Spinal kyphosis (convex curvature) or lordosis (concave curvature)
- Varus (bowleg) or valgus (knock knee) deformities
- Frequent ear infections (due to Eustachian tube blockages), sleep apnea (which can be central or obstructive), and hydrocephalus
Children with achondroplasia often have less muscle tone; because of this it is common for them to have delayed walking and motor skills. It is also common for children to have bowed legs, scoliosis, lordosis, arthritis, issues with joint flexibility, breathing problems, ear infections, and crowded teeth. These issues can be treated with surgery, braces, or physical therapy.
Hydrocephalus is a severe effect associated with achondroplasia in children. This condition occurs when cerebrospinal fluid is not able to flow in and out of the skull because of how the spine narrows. This fluid build up is associated with an enlarged head, vomiting, lethargy, headaches, and irritability. A shunt surgery is commonly performed to treat this condition, but an endoscopic third ventriculostomy can also be done.
Adults with achondroplasia often face issues with obesity and sleep apnea. It is also typical for adults to experience numbness or tingling in their legs because of nerve compression.
Pregnancy in women with achondroplasia is considered higher risk. Women with achondroplasia generally have their babies delivered through C-sections to prevent complications that could occur with a natural birth.
Achondroplasia is caused by a mutation in fibroblast growth factor receptor 3 (FGFR3) gene. This gene is mainly responsible for making the protein, fibroblast growth factor receptor 3. This protein contributes to the production of collagen and other structural components in tissues and bones. When the FGFR3 gene is mutated it interferes with how this protein interacts with growth factors leading to complications with bone production. Cartilage is not able to fully develop into bone, causing the individual to be disproportionately shorter in height.
In normal development FGFR3 has a negative regulatory effect on bone growth. In achondroplasia, the mutated form of the receptor is constitutively active and this leads to severely shortened bones. The effect is genetically dominant, with one mutant copy of the FGFR3 gene being sufficient to cause achondroplasia, while two copies of the mutant gene are invariably fatal (recessive lethal) before or shortly after birth (known as a lethal allele). This occurs due to respiratory failure from an underdeveloped ribcage. A person with achondroplasia thus has a 50% chance of passing dwarfism to each of their offspring. People with achondroplasia can be born to parents that do not have the condition due to spontaneous mutation.
Achondroplasia can be inherited through autosomal dominance. In couples where one partner has achondroplasia there is a 50% chance of passing the disorder on to their child every pregnancy. In situations where both parents have achondroplasia there is a 50% chance the child will have achondroplasia, 25% chance the child will not, and a 25% chance that the child will inherit the gene from both parents resulting in double dominance and leading to severe or lethal bone dysplasia.
Studies have demonstrated that new gene mutations for achondroplasia are exclusively inherited from the father and occur during spermatogenesis; it has been theorized that sperm carrying the mutation in FGFR3 have a selective advantage over sperm with normal FGFR3. The frequency of mutations in sperm leading to achondroplasia increases in proportion to paternal age, as well as in proportion to exposure to ionizing radiation. The occurrence rate of achondroplasia in the children of fathers over 50 years of age is 1 in 1,875, compared to 1 in 15,000 in the general population. Research by urologist Harry Fisch of the Male Reproductive Center at Columbia Presbyterian Hospital in 2013 indicated that in humans this defect may be exclusively inherited from the father and becomes increasingly probable with paternal age, specifically males reproducing after 35.
Achondroplasia can be detected before birth by prenatal ultrasound. A DNA test can be performed before birth to detect homozygosity, wherein two copies of the mutant gene are inherited, a lethal condition leading to stillbirths. Clinical features include megalocephaly, short limbs, prominent forehead, thoracolumbar kyphosis and mid-face hypoplasia. Complications like dental malocclusion, hydrocephalus and repeated otitis media can be observed. The risk of death in infancy is increased due to the likelihood of compression of the spinal cord with or without upper airway obstruction.
A skeletal survey is useful to confirm the diagnosis of achondroplasia. The skull is large, with a narrow foramen magnum, and relatively small skull base. The vertebral bodies are short and flattened with relatively large intervertebral disk height, and there is congenitally narrowed spinal canal. The iliac wings are small and squared, with a narrow sciatic notch and horizontal acetabular roof. The tubular bones are short and thick with metaphyseal cupping and flaring and irregular growth plates. Fibular overgrowth is present. The hand is broad with short metacarpals and phalanges, and a trident configuration. The ribs are short with cupped anterior ends. If the radiographic features are not classic, a search for a different diagnosis should be entertained. Because of the extremely deformed bone structure, people with achondroplasia are often "double jointed". The diagnosis can be made by fetal ultrasound by progressive discordance between the short femur length and biparietal diameter by age. The trident hand configuration can be seen if the fingers are fully extended.
Another distinct characteristic of the syndrome is thoracolumbar gibbus in infancy.
There is no known cure for achondroplasia even though the cause of the mutation in the growth factor receptor has been found. Although used by those without achondroplasia to aid in growth, human growth hormone does not help people with achondroplasia, which involve a different hormonal pathway. Usually, the best results appear within the first and second year of therapy. After the second year of growth hormone therapy, beneficial bone growth decreases, so the therapy is not a satisfactory long-term treatment.
Achondroplasia is one of several congenital conditions with similar presentations, such as osteogenesis imperfecta, multiple epiphyseal dysplasia tarda, achondrogenesis, osteopetrosis, and thanatophoric dysplasia. This makes estimates of prevalence difficult, with changing and subjective diagnostic criteria over time. One detailed and long-running study in the Netherlands found that the prevalence determined at birth was only 1.3 per 100,000 live births. Another study at the same time found a rate of 1 per 10,000.
Based on their disproportionate dwarfism, some dog breeds traditionally have been classified as "achondroplastic". This is the case for the dachshund, basset hound, corgi and bulldog breeds. Data from whole genome association studies in short-limbed dogs reveal a strong association of this trait with a retro-gene coding for fibroblast growth factor 4 (FGF4). Therefore, it seems unlikely that dogs and humans are achondroplastic for the same reasons. However, histological studies in some achondroplastic dog breeds have shown altered cell patterns in cartilage that are very similar to those observed in humans exhibiting achondroplasia.
A similar form of achondroplasia was found in a litter of piglets from a phenotypically normal Danish sow. The dwarfism was inherited dominant in the offspring from this litter. The piglets were born phenotypically normal, but became more and more symptomatic as they reached maturity. This involved a mutation of the protein collagen, type X, alpha 1, encoded by the COL10A1 gene. In humans a similar mutation (G595E) has been associated with Schmid metaphyseal chondrodysplasia (SMCD), a relatively mild skeletal disorder that is also associated with dwarfism.
The now-extinct Ancon sheep was created by humans through the selective breeding of common domestic sheep with achondroplasia. The average-sized torso combined with the relatively smaller legs produced by achondroplasia was valued for making affected sheep less likely to escape without affecting the amount of wool or meat each sheep produced.
- "Achondroplasia". Oxford Dictionaries UK English Dictionary. Oxford University Press. n.d. Retrieved 20 January 2016.
- "Achondroplasia". Merriam-Webster Dictionary.
- "Achondroplasia". Genetics Home Reference. May 2012. Retrieved 12 December 2017.
- Horton, William A; Hall, Judith G; Hecht, Jacqueline T (July 2007). "Achondroplasia". The Lancet. 370 (9582): 162–172. doi:10.1016/S0140-6736(07)61090-3. PMID 17630040. S2CID 208788746.
- Pauli, RM; Adam, MP; Ardinger, HH; Pagon, RA; Wallace, SE; Bean, LJH; Mefford, HC; Stephens, K; Amemiya, A; Ledbetter, N (2012). "Achondroplasia". GeneReviews. PMID 20301331.
- "Achondroplasia". Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. 2016. Retrieved 12 December 2017.
- "Trident hand". Radiopaedia. Retrieved 31 May 2022.
- "Dwarfism". kidshealth.org. Retrieved 26 September 2018.
- "Achondroplasia | Genetic and Rare Diseases Information Center (GARD) – an NCATS Program". rarediseases.info.nih.gov. Retrieved 26 September 2018.
- Kieffer, Sara. "Achondroplasia | Johns Hopkins Pediatric Neurosurgery". Retrieved 26 September 2018.
- "Hydrocephalus – Diagnosis and treatment – Mayo Clinic". www.mayoclinic.org. Retrieved 26 September 2018.
- Services, Department of Health & Human. "Dwarfism". Retrieved 26 September 2018.
- "Learning About Achondroplasia". National Human Genome Research Institute (NHGRI). Retrieved 26 September 2018.
- Reference, Genetics Home. "FGFR3 gene". Genetics Home Reference. Retrieved 26 September 2018.
- Richette P, Bardin T, Stheneur C (2007). "Achondroplasia: From genotype to phenotype". Joint Bone Spine. 75 (2): 125–30. doi:10.1016/j.jbspin.2007.06.007. PMID 17950653.
- "Achondroplasia". Retrieved 26 September 2018.
- Wyrobek AJ, Eskenazi B, Young S, Arnheim N, Tiemann-Boege I, Jabs EW, Glaser RL, Pearson FS, Evenson D (2006). "Advancing age has differential effects on DNA damage, chromatin integrity, gene mutations, and aneuploidies in sperm". Proceedings of the National Academy of Sciences of the United States of America. 103 (25): 9601–9606. Bibcode:2006PNAS..103.9601W. doi:10.1073/pnas.0506468103. PMC 1480453. PMID 16766665.
- Kovac, Jason R; Addai, Josephine; Smith, Ryan P; Coward, Robert M; Lamb, Dolores J; Lipshultz, Larry I (November 2013). "The effects of advanced paternal age on fertility". Asian Journal of Andrology. 15 (6): 723–728. doi:10.1038/aja.2013.92. PMC 3854059. PMID 23912310.
- Harry Fisch (24 September 2013). The Male Biological Clock: The Startling News About Aging, Sexuality, and Fertility in Men. Simon and Schuster. pp. 11–. ISBN 978-1-4767-4082-9.
- Beattie, R.M.; Champion, M.P., eds. (2004). Essential questions in paediatrics for MRCPCH (1st ed.). Knutsford, Cheshire: PasTest. ISBN 978-1-901198-99-7.
- EL-Sobky, TA; Shawky, RM; Sakr, HM; Elsayed, SM; Elsayed, NS; Ragheb, SG; Gamal, R (15 November 2017). "A systematized approach to radiographic assessment of commonly seen genetic bone diseases in children: A pictorial review". J Musculoskelet Surg Res. 1 (2): 25. doi:10.4103/jmsr.jmsr_28_17. S2CID 79825711.
- "Achondroplasia Pelvis". Archived from the original on 22 October 2007. Retrieved 28 November 2007.
- Vajo, Zoltan; Francomano, Clair A.; Wilkin, Douglas J. (1 February 2000). "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". Endocrine Reviews. 21 (1): 23–39. doi:10.1210/edrv.21.1.0387. PMID 10696568.
- Aviezer, David; Golembo, Myriam; Yayon, Avner (30 June 2003). "Fibroblast Growth Factor Receptor-3 as a Therapeutic Target for Achondroplasia - Genetic Short Limbed Dwarfism". Current Drug Targets. 4 (5): 353–365. doi:10.2174/1389450033490993. PMID 12816345.
- Savarirayan, Ravi; Tofts, Louise; Irving, Melita; Wilcox, William; Bacino, Carlos A.; Hoover-Fong, Julie; Font, Rosendo Ullot; Harmatz, Paul; Rutsch, Frank; Bober, Michael B.; Polgreen, Lynda E.; Ginebreda, Ignacio; Mohnike, Klaus; Charrow, Joel; Hoernschemeyer, Daniel; Ozono, Keiichi; Alanay, Yasemin; Arundel, Paul; Kagami, Shoji; Yasui, Natsuo; White, Klane K.; Saal, Howard M.; Leiva-Gea, Antonio; Luna-González, Felipe; Mochizuki, Hiroshi; Basel, Donald; Porco, Dania M.; Jayaram, Kala; Fisheleva, Elena; Huntsman-Labed, Alice; Day, Jonathan (5 September 2020). "Once-daily, subcutaneous vosoritide therapy in children with achondroplasia: a randomised, double-blind, phase 3, placebo-controlled, multicentre trial". The Lancet. 396 (10252): 684–692. doi:10.1016/S0140-6736(20)31541-5. PMID 32891212. S2CID 221472752.
- Kitoh H, Kitakoji T, Tsuchiya H, Katoh M, Ishiguro N (2007). "Distraction osteogenesis of the lower extremity in patients that have achondroplasia/hypochondroplasia treated with transplantation of culture-expanded bone marrow cells and platelet-rich plasma". J Pediatr Orthop. 27 (6): 629–34. doi:10.1097/BPO.0b013e318093f523. PMID 17717461. S2CID 42226362.
- Online Mendelian Inheritance in Man (OMIM): ACHONDROPLASIA; ACH - 100800
- Savarirayan, Ravi (4 July 2019). "C-Type Natriuretic Peptide Analogue Therapy in Children with Achondroplasia". New England Journal of Medicine. 381 (1): 25–35. doi:10.1056/NEJMoa1813446. PMID 31269546.
- Jones, T.C.; Hunt, R.D. (1979). "The musculoskeletal system". In Jones, T.C.; Hunt, R.D.; Smith, H.A. (eds.). Veterinary Pathology (5th ed.). Philadelphia: Lea & Febiger. pp. 1175–6. ISBN 978-0812107890.
- Willis M.B. (1989). "Inheritance of specific skeletal and structural defects". In Willis M.B. (ed.). Genetics of the Dog. Great Britain: Howell Book House. pp. 119–120. ISBN 978-0876055519.
- Parker HG, VonHoldt BM, Quignon P, et al. (August 2009). "An expressed fgf4 retrogene is associated with breed-defining chondrodysplasia in domestic dogs". Science. 325 (5943): 995–8. Bibcode:2009Sci...325..995P. doi:10.1126/science.1173275. PMC 2748762. PMID 19608863.
- Braund KG, Ghosh P, Taylor TK, Larsen LH (September 1975). "Morphological studies of the canine intervertebral disc. The assignment of the beagle to the achondroplastic classification". Res. Vet. Sci. 19 (2): 167–72. doi:10.1016/S0034-5288(18)33527-6. PMID 1166121.
- Nielsen VH, Bendixen C, Arnbjerg J, et al. (December 2000). "Abnormal growth plate function in pigs carrying a dominant mutation in type X collagen". Mamm. Genome. 11 (12): 1087–92. doi:10.1007/s003350010212. PMID 11130976. S2CID 2786778.
- Gidney, Louisa (May–June 1019). "Earliest Archaeological Evidence of the Ancon Mutation in Sheep from Leicester, UK". International Journal of Osteoarchaeology. 15 (27): 318–321. doi:10.1002/oa.872. ISSN 1099-1212.
|Look up achondroplasia in Wiktionary, the free dictionary.|