polysyndactyly

Presentations of polysyndactyly vary in location and size of the duplicated digit, and in the extent of webbing between digits.{{Cite book | vauthors = Stevenson RE |url=https://www.worldcat.org/oclc/936298415 |title=Human Malformations and Related Anomalies. |date=2015 |publisher=Oxford University Press |others=Judith G. Hall, David B. Everman |isbn=978-0-19-938604-8 |location=Cary |oclc=936298415}}{{cite journal | vauthors = Chen W, Chen L, Huang W, Tian X | title = Aesthetic and Anatomic Reconstruction of Polysyndactyly of the Fifth Toe Fused With the Fourth Toe | journal = Annals of Plastic Surgery | volume = 86 | issue = 3 | pages = 323–328 | date = March 2021 | pmid = 32568755 | doi = 10.1097/SAP.0000000000002437 | s2cid = 219982668 }}

The extra digit is most commonly postaxial,{{cite journal | vauthors = Ko KR, Shim JS, Kang J, Park J | title = Surgical Outcomes and Predictive Factors of Medial Toe Excision for Polysyndactyly of the Fifth Toe | journal = Foot & Ankle International | volume = 42 | issue = 5 | pages = 562–569 | date = May 2021 | pmid = 33198478 | doi = 10.1177/1071100720971289 | s2cid = 226990510 }} on the same side as the pinky or little toe. Preaxial polysyndactyly, in which the duplicated digit is on the side of the thumb or big toe, is less common. Crossed polysyndactyly, in which polysyndactyly is present on the hand and foot, and is preaxial on one and postaxial on the other, is extremely rare and often occurs with other genetic disorders.{{cite journal | vauthors = Dewan P, Agarwal N, Dewan P, Batta V | title = Familial crossed polysyndactyly in four generations of an Indian family | journal = World Journal of Pediatrics | volume = 6 | issue = 2 | pages = 177–180 | date = May 2010 | pmid = 20127219 | doi = 10.1007/s12519-010-0020-7 | s2cid = 11914996 }}

Polysyndactyly may be classified by the level of duplication. The extra digit may be small and comprise only soft tissue,{{cite journal | vauthors = Woo SJ, Kim BJ, Kwon ST | title = Case-control study of the treatment of postaxial polysyndactyly of the foot: Comparison of surgical results after removal of the fifth or sixth toe | journal = Archives of Plastic Surgery | volume = 48 | issue = 1 | pages = 91–97 | date = January 2021 | pmid = 33503751 | pmc = 7861990 | doi = 10.5999/aps.2020.01620 }} but usually includes at least one bone, most commonly the distal and middle phalanges.{{cite journal | vauthors = Bae K, Kang MS, Kim TH, Park SS | title = Classification of Middle Phalangeal Postaxial Polysyndactyly Based on Intraoperative Arthrography Is Useful for Surgical Decision-making in Children Younger Than 2 Years | journal = Journal of Pediatric Orthopedics | volume = 41 | issue = 7 | pages = 437–443 | date = May 2021 | pmid = 33999568 | doi = 10.1097/BPO.0000000000001858 | s2cid = 234768434 }} Partial or complete duplication of the proximal phalanx, metacarpal or metatarsal can also occur.

Fusing of the extra digit may be incomplete, giving the appearance of the extra digit being partially connected to the (otherwise normal) adjacent digit. However, complete fusion of the extra digit to the adjacent digit, via soft tissue and skin, is more common.

Polysyndactyly is typically inherited, in an autosomal dominant pattern.{{cite journal | vauthors = Saygin D, Tabib T, Bittar HE, Valenzi E, Sembrat J, Chan SY, Rojas M, Lafyatis R | display-authors = 6 | title = Transcriptional profiling of lung cell populations in idiopathic pulmonary arterial hypertension | journal = Pulmonary Circulation | volume = 10 | issue = 1 | pages = 73–92 | date = March 1985 | pmid = 32166015 | doi = 10.1111/j.1741-4520.1985.tb00636.x | pmc = 7052475 | doi-access = free }} The specific mutations leading to polysyndactyly are varied between among types of the condition and different families. However, many cases are caused by changes to genetic elements affecting the signaling molecule Sonic Hedgehog (SHH). Primarily, mutations are found in the zone of polarizing activity regulatory sequence, or ZRS, that controls the expression of SHH in developing limbs. Many cases of polysyndactyly are the result of duplications of the ZRS{{cite journal | vauthors = Xu J, Wu J, Teng X, Cai L, Yuan H, Chen X, Hu M, Wang X, Jiang N, Chen H | display-authors = 6 | title = Large duplication in LMBR1 gene in a large Chinese pedigree with triphalangeal thumb polysyndactyly syndrome | journal = American Journal of Medical Genetics. Part A | volume = 182 | issue = 9 | pages = 2117–2123 | date = September 2020 | pmid = 32662247 | doi = 10.1002/ajmg.a.61757 | s2cid = 220518629 }}{{cite journal | vauthors = Lohan S, Spielmann M, Doelken SC, Flöttmann R, Muhammad F, Baig SM, Wajid M, Hülsemann W, Habenicht R, Kjaer KW, Patil SJ, Girisha KM, Abarca-Barriga HH, Mundlos S, Klopocki E | display-authors = 6 | title = Microduplications encompassing the Sonic hedgehog limb enhancer ZRS are associated with Haas-type polysyndactyly and Laurin-Sandrow syndrome | journal = Clinical Genetics | volume = 86 | issue = 4 | pages = 318–325 | date = October 2014 | pmid = 24456159 | doi = 10.1111/cge.12352 | hdl = 11858/00-001M-0000-0025-B3BA-6 | s2cid = 27700015 | hdl-access = free }}{{cite journal | vauthors = Dai L, Guo H, Meng H, Zhang K, Hu H, Yao H, Bai Y | title = Confirmation of genetic homogeneity of syndactyly type IV and triphalangeal thumb-polysyndactyly syndrome in a Chinese family and review of the literature | journal = European Journal of Pediatrics | volume = 172 | issue = 11 | pages = 1467–1473 | date = November 2013 | pmid = 23793141 | doi = 10.1007/s00431-013-2071-y | s2cid = 40376029 }} or the nearby pre-ZRS region.{{cite journal | vauthors = Potuijt JW, Baas M, Sukenik-Halevy R, Douben H, Nguyen P, Venter DJ, Gallagher R, Swagemakers SM, Hovius SE, van Nieuwenhoven CA, Galjaard RH, van der Spek PJ, Ahituv N, de Klein A | display-authors = 6 | title = A point mutation in the pre-ZRS disrupts sonic hedgehog expression in the limb bud and results in triphalangeal thumb-polysyndactyly syndrome | journal = Genetics in Medicine | volume = 20 | issue = 11 | pages = 1405–1413 | date = November 2018 | pmid = 29543231 | doi = 10.1038/gim.2018.18 | doi-access = free }}{{cite journal | vauthors = Potuijt JW, Sowinska-Seidler A, Bukowska-Olech E, Nguyen P, Jankowski A, Magielsen F, Matuszewska K, van Nieuwenhoven CA, Galjaard RH, de Klein A, Jamsheer A | display-authors = 6 | title = The pZRS non-coding regulatory mutation resulting in triphalangeal thumb-polysyndactyly syndrome changes the pattern of local interactions | journal = Molecular Genetics and Genomics | volume = 297 | issue = 5 | pages = 1343–1352 | date = September 2022 | pmid = 35821352 | doi = 10.1007/s00438-022-01921-2 | s2cid = 250492417 }}

Polysyndactyly can be associated with the presence of other genetic disorders. It is a hallmark of Carpenter's syndrome, an autosomal recessive disorder that is also associated with craniosynostosis, obesity, short stature, and other malformations.{{Cite journal | vauthors = Temtamy SA |date=1 July 1966 |title=Carpenter's syndrome: Acrocephalopolysyndactyly. An autosomal recessive syndrome |journal=The Journal of Pediatrics |language=en |volume=69 |issue=1 |pages=111–120 |doi=10.1016/S0022-3476(66)80368-2|pmid=5935752 }} Patients with other syndromes, including Pallister-Hall syndrome{{cite journal | vauthors = Consales A, Ardemani G, Cinnante CM, Catalano MR, Giavoli C, Villa R, Iascone M, Fontana C, Bedeschi MF, Fumagalli M | display-authors = 6 | title = Neuroimaging appearance of hypothalamic hamartomas in monozygotic twins with Pallister-Hall syndrome: case report and review of the literature | journal = BMC Neurology | volume = 22 | issue = 1 | pages = 118 | date = March 2022 | pmid = 35331151 | pmc = 8943937 | doi = 10.1186/s12883-022-02618-0 | doi-access = free }} and Greig cephalopolysyndactyly syndrome{{cite journal | vauthors = Biesecker LG | title = The Greig cephalopolysyndactyly syndrome | journal = Orphanet Journal of Rare Diseases | volume = 3 | issue = 1 | pages = 10 | date = April 2008 | pmid = 18435847 | pmc = 2397380 | doi = 10.1186/1750-1172-3-10 | doi-access = free }} may also display polysyndactyly of varying severity.

Polysyndactyly has full penetrance but variable expressivity; individuals who possess an allele for polysyndactyly may have a different severity of the condition. This has been seen in case studies where a parent has hexadactyly in their 4th and 5th fingers but their child has hexadactyly in their 1st, 2nd, 3rd and 4th fingers.{{cite journal | vauthors = Fried K, Mundel G | title = Polysyndactyly and Marfan's syndrome | journal = Journal of Medical Genetics | volume = 11 | issue = 2 | pages = 141–144 | date = June 1974 | pmid = 4366482 | pmc = 1013109 | doi = 10.1136/jmg.11.2.141 }}

Polysyndactyly can be diagnosed in utero through sonographic and genetic testing, though sonography may be preferred due to the cost and risk associated with genetic testing.{{cite journal | vauthors = Zhang SJ, Lin HB, Jiang QX, He SZ, Lyu GR | title = Prenatal diagnosis of triphalangeal thumb-polysyndactyly syndrome by ultrasonography combined with genetic testing: A case report | journal = World Journal of Clinical Cases | volume = 9 | issue = 23 | pages = 6832–6838 | date = August 2021 | pmid = 34447832 | pmc = 8362503 | doi = 10.12998/wjcc.v9.i23.6832 | doi-access = free }} Ultrasounds, typically done at the 14th to 16th week of pregnancy, can detect the presence of extra metacarpals, metatarsals, or phalanges.{{cite journal | vauthors = Zimmer EZ, Bronshtein M | title = Fetal polydactyly diagnosis during early pregnancy: clinical applications | language = English | journal = American Journal of Obstetrics and Gynecology | volume = 183 | issue = 3 | pages = 755–758 | date = September 2000 | pmid = 10992205 | doi = 10.1067/mob.2000.106974 }} Genetic testing of the fetus examines disruptions in the HOXD13 gene at 2q31-q32 and in the GLI3 gene at 7p13. These genomic regions regulate proliferation and differentiation in the limb bud, and can lead to phenotypic anomalies, including polysyndactyly, if mutated. Postnatally, polysyndactyly is diagnosed by observation of an extra digit and X-rays to confirm the presence of an extra metacarpal, metatarsal, or phalanx.{{cite book | chapter = Polysyndactyly |date=2008 | title = Encyclopedia of Genetics, Genomics, Proteomics and Informatics |pages=1535 | veditors = Rédei GP |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-1-4020-6754-9_13251 |isbn=978-1-4020-6754-9 |s2cid=239943368 }}

Polysyndactyly is treated through surgical excision of the extra digit. The choice of which digit to remove affects post-operative outcomes; factors that must be considered when determining which digit to excise include the neurovascular bundles, angle differences, risks for impaired circulation, post-operative appearance, and residual deformities.

Treatment is generally aimed at normalizing both function and appearance of the affected extremity and, in the case of polysyndactyly of the foot, shoe fit and comfort.{{cite journal | vauthors = Burger E, 't Hart J, Hovius S, Van Nieuwenhoven C | title = Quality of life in children with preaxial polydactyly of the foot in comparison to adults, postaxial polydactyly and healthy controls | journal = Journal of Pediatric Orthopedics. Part B | volume = 31 | date = September 2022 | issue = 1 | pages = 27–33 | pmid = 36125884 | doi = 10.1097/BPB.0000000000001004 | s2cid = 252382615 }} The underlying cause of polysyndactyly determines the overall quality of life for individuals diagnosed with this condition. If there are no comorbid or underlying genetic conditions, surgical removal of the extra digit generally results in a high quality of life. Parents of children with polysyndactyly have reported high physical, social, emotional, and school functioning and good psychosocial health after removal of the extra digit.{{cite journal | vauthors = Gao Q, Wang S, Ren J, Wen X | title = Measuring parent proxy-reported quality of life of 11 rare diseases in children in Zhejiang, China | journal = Health and Quality of Life Outcomes | volume = 18 | issue = 1 | pages = 372 | date = November 2020 | pmid = 33225969 | pmc = 7682005 | doi = 10.1186/s12955-020-01572-0 | doi-access = free }}

{{Reflist}}

• [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1013109/ Polysyndactyly and Marfan's syndrome] The case of an Egyptian Jewish family with 17 affected members. The mother also had Marfan's syndrome, which she passed on to a daughter who did not have polysyndactyly.

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Category:Congenital disorders of musculoskeletal system

Category:Fingers

Category:Supernumerary body parts