Polydactyly#Other animals

In humans/animals this condition can present itself on one or both hands or feet.{{Cite journal |last1=Hirota |first1=Yuka |last2=Ueda |first2=Koichi |last3=Umeda |first3=Chizuru |last4=Yoshida |first4=Eriko |date=2022-11-03 |title=New Notations for Better Morphological Distinction of Postaxial Polydactyly of the Foot |journal=Plastic and Reconstructive Surgery Global Open |volume=10 |issue=11 |pages=e4504 |doi=10.1097/GOX.0000000000004504 |issn=2169-7574 |pmc=9633084 |pmid=36348750}} The extra digit is usually a small piece of soft tissue that can be removed. Occasionally it contains bone without joints; rarely it may be a complete functioning digit. The extra digit is most common on the ulnar (little finger) side of the hand, less common on the radial (thumb) side, and very rarely within the middle three digits. These are respectively known as postaxial (little finger), preaxial (thumb), and central (ring, middle, index fingers) polydactyly. The extra digit is most commonly an abnormal fork in an existing digit, or it may rarely originate at the wrist as a normal digit does.{{cite web|last=Eaton|first=Charles|title=Polydactyly (Extra Fingers)|url=http://www.eatonhand.com/hw/hw024.htm|access-date=9 February 2010}}

Polydactyly can be divided into three major types, which are discussed below, which depend on the location of the additional digit.{{Cite journal |last1=Watanabe |first1=H. |last2=Fujita |first2=S. |last3=Oka |first3=I. |date=1992-05-01 |title=Polydactyly of the foot: an analysis of 265 cases and a morphological classification |url=https://pubmed.ncbi.nlm.nih.gov/1561258 |journal=Plastic and Reconstructive Surgery |volume=89 |issue=5 |pages=856–877 |doi=10.1097/00006534-199205000-00014 |issn=0032-1052 |pmid=1561258|s2cid=20651470 }}

In 2019 it was found that in cases of polydactyly with a fully functional additional digit, muscles to control the extra digit may be duplicated, resulting in increased motor control that allows the patient to carry out certain tasks with one hand that would normally require two.{{Cite web |title=Six fingers per hand: A congenital additional finger brings motor advantages — Bernstein Center Freiburg |url=https://www.bcf.uni-freiburg.de/news/2019/190603-mehring |access-date=2022-11-16 |website=www.bcf.uni-freiburg.de |language=en}}{{Cite web |title=Six fingers per hand — Office of University and Science Communications |url=https://kommunikation.uni-freiburg.de/pm-en/press-releases-2019/six-fingers-per-hand |access-date=2022-11-16 |website=kommunikation.uni-freiburg.de |language=en}}

File:Polydactyly (cropped).jpg|Male with unilateral preaxial polydactyly affecting the left thumb. The supernumerary digit had normal sensation but no joint and hence could not move independently.

File:Polydactyly Left Hand.jpg|Type 1 ulnar polydactyly. An extra digit is attached by skin and nerves.

File:Preaxial polydactyly right hand.jpg|Preaxial polydactyly

File:Polydactyly postaxial.gif

This is the most common situation, in which the extra digit is on the ulnar side of the hand, thus the side of the little finger. This can also be called postaxial polydactyly. It can manifest itself very subtly, for instance only as a nubbin on the ulnar side of the little finger, or very distinctly, as a fully developed finger. Most commonly, the extra finger is rudimentary, consisting of an end phalanx with a nail, and connected to the hand with a small skin pedicle. Mostly one neurovascular bundle can be identified, with no tendons present in the extra digit. In case of a fully developed extra finger, the duplication usually presents itself at the level of the metacarpophalangeal joint. A triplication of the little finger is very rare. Ulnar polydactyly occurs ten times more often in African populations.{{cite journal |last1=Buck-Gramcko |first1=Dieter |title=Congenital malformations of the hand and forearm |journal=Chirurgie de la Main |date=January 2002 |volume=21 |issue=2 |pages=70–101 |doi=10.1016/s1297-3203(02)00103-8 |pmid=11980346 }} The incidence in Caucasians is reported as 1 in 1,339 live births, compared with 1 in 143 live births in Africans. Ulnar polydactyly is also often part of a syndrome. In patients with African ancestry ulnar polydactyly mostly occurs isolated, whereas the presentation in Caucasians is often associated with a syndrome, though in a retrospective review, only 4 of 37 cases of ulnar polydactyly in Caucasians were syndromic.{{cite journal |last1=Rayan |first1=Ghazi M. |last2=Frey |first2=Bret |title=Ulnar Polydactyly |journal=Plastic and Reconstructive Surgery |date=May 2001 |volume=107 |issue=6 |pages=1449–1454 |doi=10.1097/00006534-200105000-00021 |pmid=11335816 |s2cid=25012153 }}

File:Polydactyly preaxial.gif

This is a less common situation, in which the affectation is on the side of the hand towards the thumb. Radial polydactyly refers to the presence of an extra digit (or extra digits) on the radial side of the hand. It is most frequent in Indian populations and it is the second most common congenital hand disorder. The incidence of radial polydactyly is reported as 1 in every 3,000 live births.{{Cite book|author=Jobe MT |chapter= Congenital Anomalies of the Hand |title= Campbell's Operative Orthopaedics |editor1=Canale ST|editor2= Beaty JH |volume=11 |pages=4367–4449 |year=2008 |doi=10.1016/b978-0-323-03329-9.50079-9|isbn= 9780323033299 }} The clinical features of radial polydactyly will depend upon the extent of duplication.

Radial polydactyly varies from a barely visible radial skin tag to complete duplication. Thumb polydactyly varies from barely visible broadening of the distal phalanx to full duplication of the thumb including the first metacarpal.{{Cite book|last=wikibooks |title=Handbook of genetic counseling/polydactyly and syndactyly| url=http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling/Polydactyly_and_Syndactyly }}

Radial polydactyly is frequently associated with several syndromes.{{cite web |title= Summary of most common syndromes with concomitant polydactyly |url=http://www.orthobullets.com/hand/6079/polydactyly}}

This is a rare condition, in which the extra digit is on the ring, middle or index finger. Of these fingers, the index finger is most often affected, whereas the ring finger is rarely affected.{{cite web |title= Pictures of Extra Fingers |language=nl|url=http://www.erasmusmc.nl/plastischechirurgie/patientenzorg1/handenteam_sophia/aand/polydactylie/2154496/|archive-url=https://web.archive.org/web/20131111113033/https://www.erasmusmc.nl/plastischechirurgie/patientenzorg1/handenteam_sophia/aand/polydactylie/2154496/|archive-date=11 November 2013}}

This type of polydactyly can be associated with syndactyly, cleft hand, and several other syndromes.{{cite journal |vauthors=Graham TJ, Ress AM |title=Finger polydactyly |journal=Hand Clin |volume=14 |issue= 1|pages=49–64 |year=1998|doi=10.1016/S0749-0712(21)00141-4 |pmid=9526156 }}{{cite journal |last1=Tada |first1=Koichi |last2=Kurisaki |first2=Eiji |last3=Yonenobu |first3=Kazuo |last4=Tsuyuguchi |first4=Yuichi |last5=Kawai |first5=Hideo |title=Central polydactyly—A review of 12 cases and their surgical treatment |journal=The Journal of Hand Surgery |date=September 1982 |volume=7 |issue=5 |pages=460–465 |doi=10.1016/s0363-5023(82)80040-3 |pmid=7130654 }}

Polysyndactyly presents various degrees of syndactyly affecting fingers three and four.

File:Shh ectopic expression.gif

Polydactyly is associated with different mutations, either mutations in a gene itself or in a cis-regulatory element responsible for the expression of a specific gene. Mutations in Hoxa- or Hoxd clusters are reported leading to polydactyly. Interactions of Hoxd13 and GLI3 induce synpolydactyly, a combination of extra and consolidated digits. Other signal transduction pathways in this context are the Wnt signaling pathway or Notch.Lange, Axel, Nemeschkal, Hans L., Müller, Gerd B. (2014) Biased polyphenism in polydactylous cats carrying a single point mutation: the Hemingway model for of digit novelty. Evolutionary Biology, 41 (2), 262-275, 29, 2014 doi:10.1007/s11692-013-9267-y

In the specific case of preaxial polydactyly (Hemingway mutant), a cis-acting mutation approximately 1Mb upstream of SHH gene has been implicated.{{cite journal |vauthors=Lettice LA, Heaney SJ, Purdie LA, Li L, de Beer P, Oostra BA, Goode D, Elgar G, Hill RE, de Graaff E |title=A long-range Shh enhancer regulates expression in the developing limb and fin and is associated with preaxial polydactyly |journal=Human Molecular Genetics |volume=12 |issue=14 |pages=1725–35 |year=2003 |pmid=12837695 |doi=10.1093/hmg/ddg180 |url=https://lirias.kuleuven.be/bitstream/123456789/34481/1/Shh+artikel.pdf|doi-access=free }} Normally SHH is expressed in an organiser region, called the zone of polarizing activity (ZPA) on the posterior limb side. From there it diffuses anteriorly, laterally to the growth direction of the limb. In the mutant, smaller ectopic expression in a new organiser region is seen on the anterior side of the limb. This ectopic expression causes cell proliferation delivering the raw material for one or more new digits.{{cite journal |vauthors=Lettice LA, Hill AE, Devenney PS, Hill RE |title=Point mutations in a distant sonic hedgehog cis-regulator generate a variable regulatory output responsible for preaxial polydactyly |journal=Human Molecular Genetics |volume=17 |issue=7 |pages=978–85 |year=2008 |pmid=18156157 |doi=10.1093/hmg/ddm370 |doi-access=free|hdl=20.500.11820/76c18e1b-ba87-49c6-9da7-c837187646a5 |hdl-access=free }}{{cite journal |vauthors=Lettice LA, Williamson I, Wiltshire JH, Peluso S, Devenney PS, Hill AE, Essafi A, Hagman J, Mort R, Grimes G, DeAngelis CL, Hill RE |title=Opposing functions of the ETS factor family define SHH spatial expression in limb buds and underlie polydactyly |journal=Developmental Cell |volume=22 |issue=2 |pages=459–67 |year=2012 |pmid=22340503 |pmc=3314984 |doi=10.1016/j.devcel.2011.12.010}}

Polydactyly can occur by itself, or more commonly, as one feature of a syndrome of congenital anomalies. When it occurs by itself, it is associated with autosomal dominant mutations in single genes, i.e. it is not a multifactorial trait.{{cite web|title=Polydactyly and Syndactyly|publisher=Milton S. Hershey Medical Center|url=http://www.hmc.psu.edu/healthinfo/pq/poly.htm|archive-url=https://web.archive.org/web/20100307090933/http://www.hmc.psu.edu/healthinfo/pq/poly.htm|archive-date=2010-03-07|access-date=9 February 2010}} But mutation in a variety of genes can give rise to polydactyly. Typically the mutated gene is involved in developmental patterning, and a syndrome of congenital anomalies results, of which polydactyly is one feature or two.{{citation needed|date=December 2017}}

Polydactyly has been linked to the prenatal environment in a 2020 study showing a relationship to maternal PM10 pollution exposure in China.{{cite journal |last1=Zhang |first1=Jia-Yu |last2=Gong |first2=Ting-Ting |last3=Huang |first3=Yan-Hong |last4=Li |first4=Jing |last5=Liu |first5=Shu |last6=Chen |first6=Yan-Ling |last7=Li |first7=Li-Li |last8=Jiang |first8=Cheng-Zhi |last9=Chen |first9=Zong-Jiao |last10=Wu |first10=Qi-Jun |title=Association between maternal exposure to PM10 and polydactyly and syndactyly: A population-based case-control study in Liaoning province, China |journal=Environmental Research |date=1 August 2020 |volume=187 |pages=109643 |doi=10.1016/j.envres.2020.109643 |pmid=32416360 |bibcode=2020ER....18709643Z|s2cid=218670157 }}

Types include:

Because polydactyly can be part of a syndrome (known genetic defect) or association (genetic defect not known), children with a congenital upper extremity deformity should be examined by a geneticist for other congenital anomalies. This should also be done if a syndrome is suspected, or if more than two or three generations of the family are affected.{{cite journal |vauthors=Van Nieuwenhoven C, Boehmer A, Hovius S |title=Polydactyly |journal=Praktische Pediatrie |volume=2 |year=2009}}

As of 2009, 97 genetic syndromes have been associated with different kinds of polydactyly.

Examples of syndromes include Diamond–Blackfan anemia, and the VACTERL association, acrocallosal syndrome, basal cell nevus syndrome, Biemond syndrome, ectrodactyly-ectodermal dysplasias-cleft lip/palate syndrome, mirror hand deformity, Mohr syndrome, oral-facial-digital syndrome, Rubinstein–Taybi syndrome, short rib polydactyly.{{Emedicine|article|1113584|Supernumerary Digit}}

Ulnar polydactyly is often bilateral and associated with syndactyly and polydactyly of the feet. This can be a simple or complex polydactyly. Ulnar polydactyly occurs as an isolated congenital condition, but can also be part of a syndrome, such as: Trisomy 13, Greig cephalopolysyndactyly syndrome, Meckel syndrome, Ellis–van Creveld syndrome, McKusick–Kaufman syndrome, Down syndrome, Bardet–Biedl syndrome, Smith–Lemli–Opitz syndrome.{{cite journal |last1=Nicolai |first1=JP |last2=Hamel |first2=BC |last3=Menalda |first3=GA |title=Polydactylie |trans-title=Polydactyly |language=nl |journal=Nederlands Tijdschrift voor Geneeskunde |date=27 January 1990 |volume=134 |issue=4 |pages=157–9 |pmid=2304571 |url=https://www.ntvg.nl/artikelen/polydactylie}}

Type VII of radial polydactyly is associated with several syndromes:

Holt–Oram syndrome, Fanconi anemia (aplastic anemia by the age of 6), Townes–Brocks syndrome, and Greig cephalopolysyndactyly (also known to occur with ulnar polydactyly).

The syndromes associated with central polydactyly are:

Bardet–Biedl syndrome,{{cite journal |vauthors=Kumar S, Mahajan BB, Mittal J |title=Bardet-Biedl syndrome: a rare case report from North India |journal= Indian J Dermatol Venereol Leprol |volume=78 |issue= 9|page=228 |year=2012 |doi=10.4103/0378-6323.93656 |pmid=22421669 |doi-access=free}} Meckel syndrome,{{cite journal |vauthors=Panduranga C, Kangle R, Badami R, Patil PV |title=Meckel-Gruber syndrome: Report of two cases |journal= J Neurosci Rural Pract |volume=3 |issue=1|pages=56–9 |year=2012 |doi=10.4103/0976-3147.91943|pmid=22346195 |pmc=3271618 |doi-access=free }} Pallister–Hall syndrome,{{cite book |author= Biesecker LG |title=Pallister-Hall Syndrome |year=1993}} Legius syndrome,{{cite journal |vauthors=Denayer E, Chmara M |title=Legius syndrome in fourteen families |journal=Hum. Mutat. |volume=32 |issue=1 |pages=1985–98 |year=2011 |doi=10.1002/humu.21404|pmid=21089071 |pmc=3038325}} Holt–Oram syndrome.{{cite journal |vauthors=Fryns JP, Bonnet D, De Smet L |title=Holt-Oram syndrome with associated postaxial and central polydactyly. Further evidence for genetic heterogeneity in the Holt-Oram syndrome |journal=Genet Couns|volume=7 |issue=4|pages=323–4 |year=1996 |pmid=8985738}} Central polydactyly can also be associated with syndactyly and cleft hand.

From an evo-devo point of view, polydactyly is a phenotypic variation or innovation, as the fingers and toes arise in places where nothing is phenotypically present in the wild type. Although it is initiated by a point mutation, it occurs as a polyphenism with different numbers of toes. The analysis of the additional toe numbers of Maine Coon cats revealed that the number of toes follows a developmental bias: 2 additional toes occur much more frequently than 4, these more frequently than 6 or 8 additional ones.Lange, Axel, Nemeschkal, Hans L., Müller, Gerd B. (2014) Biased polyphenism in polydactylous cats carrying a single point mutation: the Hemingway model for of digit novelty. Evolutionary Biology, 41 (2), 262-275, 29, 2014 doi:10.1007/s11692-013-9267-y Also, for the evo-devo theory, polydactyly cannot be adequately explained by genetic mutation alone, but only by constructive development, i.e. the ability of development to produce a complex phenotypic output. The corresponding symbolic generation of toes can now be shown in computer models.Lange, Axel, Nemeschkal, Hans L., Müller, Gerd B. (2018) A threshold model for polydactyly. Progress in Biophysics and Molecular Biology 137, 1-11. https://doi.org/10.1016/j.pbiomolbio.2018.04.007

Classification is performed by using x-ray imaging to see the bone structures. In 1961, Frantz and O'Rahilly proposed that congenital anomalies of the limb could be classified in seven categories, based on the embryonic failure causing the clinical presentation. These categories are failure of formation of parts, failure of differentiation, duplication, overgrowth, undergrowth, congenital constriction band syndrome, and generalized skeletal abnormalities.{{cite journal |last1=Frantz |first1=Charles H. |last2=OʼRahilly |first2=Ronan |title=Congenital Skeletal Limb Deficiencies |journal=The Journal of Bone & Joint Surgery |date=December 1961 |volume=43 |issue=8 |pages=1202–1224 |doi=10.2106/00004623-196143080-00012 |s2cid=36967129 |citeseerx=10.1.1.975.8614 }} In 1976 this was modified by Swanson.{{cite journal |author=Swanson AB |title=A classification for congenital limb malformations |journal=J Hand Surg Am |volume=1|issue=1 |pages=8–22 |year=1976 |doi=10.1016/s0363-5023(76)80021-4 |pmid=1021591 }} Polydactyly belongs to the category of duplication.{{cite journal |vauthors=Watt AJ, Chung KC |title=Duplication |journal=Hand Clin |volume=25 |issue=2 |pages=215–227 |year=2009 |doi=10.1016/j.hcl.2009.01.001 |pmid=19380061 }} As of 2009, research has shown that the majority of congenital anomalies occur during the 4-week embryologic period of rapid limb development.

The classification of ulnar polydactyly exists of either two or three types. The two-stage classification, according to Temtamy and McKusick, involves type A and B. In type A there is an extra little finger at the metacarpophalangeal joint, or more proximal including the carpometacarpal joint. The little finger can be hypoplastic or fully developed. Type B varies from a nubbin to an extra, non-functional little finger part on a pedicle. According to the three-type classification, type I includes nubbins or floating little fingers, type II includes duplications at the MCPJ, and type III includes duplications of the entire ray.{{cite journal |vauthors=Temtamy SA, McKusick VA |title= The genetics of hand malformations |journal=Birth Defects Orig. Artic. Ser.|volume=14 |issue=3 |pages=1–619 |year=1978|pmid= 215242}}

The Wassel classification is the most widely used classification of radial polydactyly, based upon the most proximal level of skeletal duplication. The most common type is Wassel 4 (about 50% of such duplications) followed by Wassel 2 (20%) and Wassel 6 (12%).

The classification of central polydactyly is based on the extent of duplication and involves the following three types:

Type I is a central duplication, not attached to the adjacent finger by osseous or ligamentous attachments; it frequently does not include bones, joints, cartilage, or tendons.

Type IIA is a nonsyndactylous duplication of a digit or part of a digit with normal components, and articulates with a broad or bifid metacarpal or phalanx.

Type IIB is a syndactylous duplication of a digit or part of a digit with normal components, and articulates with a broad or bifid metacarpal or phalanx.

Type III is a complete digital duplication, which has a well-formed duplicated metacarpal.

File:Polydactyly_01_Lhand_AP.jpg|X-ray of type III central polydactyly. The middle fingers are the same length.

File:X-ray of feet in polydactyly.jpg|Right-sided duplication of the right little toe in an 8.5 months old male, with two toes (fifth and sixth) apparently forming joints with the fifth metatarsal bone, which is mildly broadened distally. The duplicated toes have almost normal growth. The fifth toe has mild varus angulation, and the sixth toe has substantial valgus angulation.

File:Polydactyly 01 Lfoot AP.jpg|Left foot with postaxial polydactyly of 5th ray

Ulnar polydactyly usually does not interfere with hand function, but for social reasons it can be treated operatively.

The treatment of Type A ulnar polydactyly is complex as its goal is to remove the accessory digit while maintaining a stable, functional small finger. When the duplicated proximal phalanx articulates with a common, broad metacarpal head, the ulnar collateral ligament must be considered. In those cases with a common articulation or with a sixth metacarpal the muscle executing the abduction of the little finger (abductor digiti minimi) must be preserved.

In patients with a common metacarpal articulation an elliptical incision at the base of the post-axial digit is made. This incision may be extended proximally in order to adequately expose the abductor digiti minimi. The ulnar collateral ligament and the insertions of the abductor digiti minimi are then elevated with a periosteal sleeve. The duplicated extensor and flexor tendons to the ulnar digit are transected and after that the digit is amputated at its articulation with the metacarpal. If the articular surface is wide the metacarpal may be shaved. At last the collateral ligament and abductor digiti minimi are reinserted at the base of the preserved proximal phalanx and a wire is then placed across the reconstructed joint.

In patients with a duplicated metacarpal, the accessory digit is amputated in a standard ray fashion with transfer of the abductor digiti minimi to the retained small finger.

In this situation there is an absence of osseous and ligamentous structures. The surgical technique is analogous to radial polydactyly, in which the level of duplication and anatomical components should guide operative treatment.

The pedicled ulnar extra digit can be removed by suture ligation to devise the skin bridge of the newborn child. This might be easier than an excision of the extra digit when the child is 6 to 12 months old. Ligation occludes the vascular supply to the duplicated digit, resulting in dry gangrene and subsequent autoamputation. This must be done with consideration of the presence of a neurovascular bundle, even in very small skin bridges. When the ligation is done inappropriately it can give a residual nubbin. Also, a neuroma can develop in the area of the scar. An excision can prevent the development of a residual nubbin and the sensitivity due to a neuroma.

For infants with ulnar type B polydactyly the recommended treatment is ligation in the neonatal nursery.{{unbalanced opinion|date=March 2023}}{{citation needed|date=March 2023}}

A 2011 study opined that excision of an extra digit in the neonatal nursery was a safe and simple procedure with a good clinical and cosmetic outcome.{{cite journal |vauthors=Katz K, Linder N |title= Postaxial type B polydactyly treated by excision in the neonatal nursery |journal=J Pediatr Orthop |volume=31 |issue=4 |pages=448–9 |year=2011 |doi=10.1097/bpo.0b013e31821addb6 |pmid=21572283 |s2cid=11983544 }}

As of 2022, for infants with ulnar type B polydactyly the recommended treatment is surgical excision or suture ligation, when no bony structures exist. Complications of ligation include infection, neuroma or cyst formation.{{Cite web |last1=Barnes |first1=Curtis J. |last2=De Cicco |first2=Franco L. |date=2022 |title=Supernumerary Digit |url=http://www.ncbi.nlm.nih.gov/books/NBK564405/ |location=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=33232075}}

Because neither of the two thumb components is normal, a decision should be taken on combining which elements to create the best possible composite digit. Instead of amputating the most hypoplastic thumb, preservation of skin, nail, collateral ligaments and tendons is needed to augment the residual thumb.{{cite journal |author= Light TR |title=Treatment of preaxial polydactyly |journal=Hand Clin |volume=8 |issue=1 |pages=161–75 |year=1992|doi=10.1016/S0749-0712(21)00700-9 |pmid=1572920 }} Surgery is recommended in the first year of life, generally between 9 and 15 months of age.

Surgical options depend on type of polydactyly.{{cite journal |vauthors=Tonkin MA, Bulstrode NW |title= Bilhaut-Cloquet procedure for Wassel types III, IV and VII thumb duplication |journal= J Hand Surg Eur |volume=32 |issue=6 |pages=684–93 |year=2007 |doi=10.1016/j.jhse.2007.05.021 |pmid=17993432 |s2cid=38444662 }}

This type of procedure is recommended for Wassel types 1 and 2 (in which both thumbs are severely hypoplastic) by some congenital hand surgeons.{{cite journal |author=Bilhaut M. |title=Guérison d'un pouce bifide par un nouveau procédé opératoire |trans-title=Healing of a bifid thumb by a new surgical procedure |language=fr |journal=Congrès Français de Chirurgie |volume=4 |pages=576–80 |year=1889 }} The technique contains a composite wedge resection of the central bone and soft-tissue. This will be achieved with approach of the lateral tissue of each thumb. The goal is to achieve a normal thumb, what concerns the size, which is possible. If the width of the nail bed is greater than 70% of the contralateral thumb, it may be split.{{cite journal |last1=Tada |first1=K |last2=Yonenobu |first2=K |last3=Tsuyuguchi |first3=Y |last4=Kawai |first4=H |last5=Egawa |first5=T |title=Duplication of the thumb. A retrospective review of two hundred and thirty-seven cases |journal=The Journal of Bone & Joint Surgery |date=June 1983 |volume=65 |issue=5 |pages=584–598 |doi=10.2106/00004623-198365050-00002 |pmid=6853563 }}{{cite journal |last1=Dobyns |first1=J. H. |last2=Lipscomb |first2=P. R. |last3=Cooney |first3=W. P. |title=Management of Thumb Duplication |journal=Clinical Orthopaedics and Related Research |date=May 1985 |volume=195 |issue=195 |pages=26–44 |doi=10.1097/00003086-198505000-00004 |pmid=2983920 |url=https://journals.lww.com/clinorthop/Abstract/1985/05000/Management_of_Thumb_Duplication.4.aspx }}

This type of procedure is used for all Wassel types of polydactyly and is the most commonly used technique. It is recommended in all cases of thumb duplication with a hypoplastic, less-functional thumb. Otherwise, one could consider the Bilhaut-Cloquet. The ulnar thumb is preferably preserved as it is the more developed one in most cases.

By detaching the radial collateral ligament from distal to proximal, a periosteal sleeve can be preserved.{{cite journal |last1=Manske |first1=Paul R. |title=Treatment of duplicated thumb using a ligamentous/periosteal flap |journal=The Journal of Hand Surgery |date=July 1989 |volume=14 |issue=4 |pages=728–733 |doi=10.1016/0363-5023(89)90200-1 |pmid=2754208 }}

In this way, the radial collateral band of the radial digit will function as the absent radial collateral ligament of the preserved ulnar thumb.

Elevation of the APB and FPB is performed in Wassel type 4 duplication; this can be accomplished via the periosteum or separately. As the tendons insert proximally, the elevation is performed proximally too to potentially rebalance the ulnar thumb. After the radial thumb is amputated, the ulnar elements are centralized and fixed with a Kirschner wire. In most cases, a longitudinal and sagittal osteotomy is needed to centralize the bony parts of the ulnar thumb. While the soft-tissue of the radial thumb was preserved, it is now attached to the radial side of the ulnar thumb together with the periosteal sleeve. The APB and FPB of the ablated radial thumb are attached to the distal phalanx for more stability. If necessary, the extensor pollicis longus and the flexor pollicis longus are reattached to centralize their course.

In Wassel type 5 and 6 the opponens pollicis muscle must be transferred to the ulnar metacarpal. Soft tissue with collateral ligament reconstruction is used to avoid any angular deformity in the preserved thumb. Tendon centralization is also often used for correction. Still, cases with osseous deformities may happen. To provide alignment, osteotomies are necessary to be done. This operation may need bone grafting, which is obtained from the amputated thumb.

This type is indicated when one thumb is larger proximally and the other thumb has a larger distal component. (The procedure is initially described as a way to lengthen amputated digits.) The goal is to create a functional thumb by combining less-hypoplastic components. On top plasty procedure is rarely employed in the treatment of congenital thumb duplication. It might be necessary for Wassel types 4, 5, 6.

At the level of the mid-proximal phalanx or mid-metacarpal, the distal component is transferred to the proximal component. The tendons of the distal component are preserved as the rest of the distal component is amputated. The neurovascular bundle which supplies the distal component is reserved and transferred proximally.

Early osteotomy and ligament reconstructions should be done to prevent deformities, such as angular growth deformities.

The surgical treatment of central polydactyly is highly variable. After the surgery the hand must be functional and stable, but also aesthetically pleasing. This requires intraoperative creativity and flexibility. The surgeon must also consider whether retention of a fully functional supranumerary digit is preferable to surgical intervention. In contrast, a functional, four-fingered hand achieved via ray amputation may be preferable to a five-fingered hand with a deformed or stiff reconstructed finger.

Cases of polysyndactyly are approached through a standard opposing zig-zag incision. The incision is favored toward the accessory digit, preserving extra skin for subsequent closure. Depending on the level and extent of duplication, the flexor and extensor tendons may require centralization or rebalancing. Also, the collateral ligaments must be preserved or reconstructed. Wide articular surfaces should be narrowed and phalangeal wedge osteotomies may be required to provide an axial alignment. Attention must also be given to reconstruct the intermetacarpal ligament. Furthermore, one should take in mind the provision for adequate web-space soft tissue.

Complications include: painful scarring, infection, joint instability, residual deformity, angulated growth, growth arrest, joint stiffness, and nail bed deformities. A 2014 study reported a 19% revision rate for preaxial polydactyly for pain or instability.

There are no substantive outcome studies regarding the function of these hands following surgical intervention. This is mainly caused by the fact that there is a generally normal function of these patients' hands following ablation with collateral ligament reconstruction. In a study on 27 patients undergoing surgical excision for Type A ulnar polydactyly, only one complication was noted in the form of an infection.{{cite journal |vauthors=Rayan GM, Frey B |title= Ulnar polydactyly |journal=Plast Reconstr Surg |volume=107 |issue=6 |pages=1449–54 |year=2001 |doi=10.1097/00006534-200105000-00021|pmid= 11335816 |s2cid= 25012153 }} However, no investigators have objectively reviewed functional range of motion or articular stability.

In a study on 21 patients with Type B ulnar polydactyly treated with suture ligation it was found that the duplicated digit was typically amputated at an average of 10 days and no complications of infection or bleeding were reported.{{cite journal |vauthors=Watson BT, Hennrikus WL |title=Postaxial type-B polydactyly |journal= J Bone Joint Surg Am |volume=79 |issue=1 |pages=65–8 |year=1997 |pmid=9010187 |doi=10.2106/00004623-199701000-00007 |s2cid=44848388 }}

In a large study on 105 patients treated with suture ligation an overall complication rate of 23.5% was reported, citing a residual tender or unacceptable bump in 16%, infection in 6%, and bleeding in 1% of patients.

In general, suture ligation is safe and effective when applied to appropriate cases of Type B polydactyly in which no substantial ligamentous or osseous structures are present within the pedicle. Parents should be educated as to the progression of necrosis, and that revision of residual tissue or scar may be necessary when the child is six months of age or older.

Advantages:

By combining two hypoplastic thumbs a sufficient thumb size is acquired. Furthermore, the IP and MCP joints are very stable as the collateral ligaments are not violated during reconstruction.

Disadvantages:

Violation during reconstruction can lead to growth arrest or asymmetric growth. Nail deformity could also occur after reconstruction. Although the joints are stable, restriction of flexion may be possible.

The average IP flexion in a reconstructed thumb is 55 degrees less than the contralateral thumb. MCP flexion averaged 55 degrees in reconstructed thumbs, compared to 75 degrees in the contralateral thumb.

Advantages:

The reconstructed joints tend to remain flexible. Also, it preserves the nail bed and physis, this increases the prevention of nail deformities over time.

Disadvantages:

Although surgeons try to obtain a stable thumb of appropriate size, instability of the IP and MCP joint may occur, as well as a size mismatch. Thumbs are defined as unacceptable if IP joint deviation exceeds 15 degrees, MCP joint deviation exceeds 30 degrees, and thumb size is inappropriate based on the examiner's assessment. Also, thumb size one-third greater or less than the contralateral thumb is defined as unacceptable.

No surgical outcomes studies exist for evaluating the function of the thumbs after an on-top plasty reconstruction.

Few clinical outcome studies exist regarding the treatment of central polydactyly. Tada and colleagues note that satisfactory surgical correction of central polydactyly is difficult to achieve and that outcomes are generally poor. In Tada's study, 12 patients were reviewed. All patients required secondary surgical procedures to address flexion contractures and angular deviation at the IP joint level.

However, several primary factors contribute to the complexity of central polydactyly reconstruction. Hypoplastic joints and soft tissues that predispose the reconstructed finger to joint contracture, and angular deformities as well as complex tendon anomalies, are often difficult to address. Therefore, treatment is wholly dependent on the anatomic components present, the degree of syndactyly, and the function of the duplicated finger.

The condition has an estimated occurrence of 0.3–3.6 per 1000 live births.{{cite journal |last1=Umair |first1=Muhammad |last2=Ahmad |first2=Farooq |last3=Bilal |first3=Muhammad |last4=Ahmad |first4=Wasim |last5=Alfadhel |first5=Majid |title=Clinical Genetics of Polydactyly: An Updated Review |journal=Frontiers in Genetics |date=6 November 2018 |volume=9 |page=447 |doi=10.3389/fgene.2018.00447 |pmid=30459804 |pmc=6232527 |doi-access=free }} Postaxial hand polydactyly is most frequent in the United States in Black males.{{cite web |title=Polydactyly |url=http://www.pennmedicine.org/encyclopedia/em_displayArticle.aspx?gcid=003176&ptid=1 |website=Penn Medicine |publisher=University of Pennsylvania |access-date=11 December 2021 |archive-url=https://web.archive.org/web/20110727122152/http://www.pennmedicine.org/encyclopedia/em_displayArticle.aspx?gcid=003176&ptid=1 |archive-date=27 July 2011}} Preaxial polydactyly occurs in 0.08 to 1.4 in 1,000 live births. In the United States, it is more common in White people and also relatively frequent in Native American and Asian people.{{cite journal |last1=Pérez López |first1=Laura M. |last2=Gutiérrez de la Iglesia |first2=Diego |last3=Cabrera González |first3=Marisa |title=Radial Polydactyly. What's New? |journal=Current Pediatric Reviews |date=21 August 2018 |volume=14 |issue=2 |pages=91–96 |doi=10.2174/1573396314666180124102012 |pmid=29366421 |s2cid=3629629 }} A 1994 study by Finley et al. combined data from Jefferson County, Alabama, United States, and Uppsala County, Sweden. This study found incidence of all types of polydactyly at rates of 2.3 per 1000 live births of White males, 0.6 per 1000 live births of White females, 13.5 per 1000 live births of Black males, and 11.1 per 1000 live births of Black females.

File:Nuremberg chronicles - Strange People - Twelve Fingers (XIIv).jpg]]

{{Main|Category:People with polydactyly}}

• Antonio Alfonseca, retired MLB professional baseball pitcher known as El Pulpo (Spanish for "the Octopus") for his extra digit on each extremity.{{citation needed|date=August 2020}}
• Endre Ady, Hungarian poet born with six fingers, but one was removed as a child. The poet later interpreted it as a sign of his selection (according to the ancient Hungarian belief, the táltos are born with more bones, such as six fingers).
• Brites de Almeida, a legendary Portuguese woman who killed seven hiding Castilian soldiers in her oven after the Battle of Aljubarrota, had six fingers on each hand.
• The actress Gemma Arterton was born with six fingers on each hand, the additional fingers being removed after birth.{{cite web|url=https://www.youtube.com/watch?v=R-_kKVXZcPQ| archive-url=https://ghostarchive.org/varchive/youtube/20211117/R-_kKVXZcPQ| archive-date=2021-11-17 | url-status=live|title='Gemma Arterton's Delicious Extra Fingers - Friday Night with Jonathan Ross - BBC One|website=OFFICIAL BBC YouTube channel| date=17 April 2010}}{{cbignore}}
• Robert Chambers, purported author of Vestiges of the Natural History of Creation, and his brother William had six digits on each limb.{{cite journal |last1=Lange |first1=Axel |last2=Müller |first2=Gerd B. |date=March 1, 2017 |title=Polydactyly in Development, Inheritance, and Evolution |journal=The Quarterly Review of Biology |volume=92 |issue=1 |pages=1–38 |doi=10.1086/690841 |pmid=29558608 |s2cid=3988166 }}
• Lucille Clifton, an African-American poet and civil rights advocate.{{cite news |url=https://www.nytimes.com/2012/10/12/books/the-collected-poems-of-lucille-clifton-1965-2010.html |title=Views of Life, Straightforward and Spare |last=Garner |first=Dwight |date=October 11, 2012 |work=The New York Times |access-date=January 15, 2020}}
• Zerah Colburn, American prodigious math calculating savant.{{cite book |url=https://archive.org/details/amemoirzerahcol01colbgoog |page=72 |title=A Memoir of Zerah Colburn |publisher=G. and C. Merriam |last=Colburn |first=Zerah |year=1833}}
• Calvin Choy, a Hong Konger singer and actor nicknamed "Sir One One" (Sir11) as he has six digits on his right hand.{{Cite web|title=一山還有一山高 蔡一智遇十二指叔叔嗌勁|url=https://hk.on.cc/hk/bkn/cnt/entertainment/20180311/bkn-20180311101948134-0311_00862_001.html|access-date=2021-03-23|website=on.cc東網|date=11 March 2018|language=zh-hk}}
• Fourteen members of a Da Silva family in São Paulo, Brazil, have six functional fingers on each hand (the thumb is doubled) and six toes on each foot.{{cite web |url=https://www.mirror.co.uk/news/real-life-stories/fourteen-members-same-family-12-6448609 |title= Fourteen members of the same family have all got 12 fingers and toes - and put them to good use |last=Myall |first=Steve |website= Daily Mirror |date=September 16, 2015}}
• Danny Garcia, boxing champion, has six toes on his right foot.{{cite web |url=https://bleacherreport.com/articles/2426303-boxing-champ-danny-garcia-reveals-he-has-6-toes-on-right-foot |title=Boxing Champ Danny Garcia Reveals He Has 6 Toes on Right Foot |last=Carson |first=Dan |website=Bleacher Report |language=en |access-date=January 15, 2020}}
• Yoandri Hernández Garrido, nicknamed Veinticuatro ("twenty four" in Spanish), has six fully formed fingers on both hands and six perfect toes on each foot.{{cite web |title=Interview Exclusive – Yoandri Hernandez Garrido – 24 fingers |url=https://www.youtube.com/watch?v=kHRtzohokJk | archive-url=https://web.archive.org/web/20140729074136/http://www.youtube.com/watch?v=kHRtzohokJk| archive-date=2014-07-29 | url-status=dead|publisher=Cubastyletv |access-date=January 18, 2013}}
• Hampton Hawes, jazz pianist, was born with six fingers on each hand (the extra fingers were surgically removed shortly after birth).{{cite web |last=Harrison |first=Dennis |title=Hamptom Hawes And The Fire Inside |publisher=JazzScript |url=http://www.jazzscript.co.uk/extra/art.hawes.htm |access-date=February 9, 2010 |archive-url=https://web.archive.org/web/20101215110955/http://www.jazzscript.co.uk/extra/art.hawes.htm |archive-date=December 15, 2010 |url-status=usurped}}
• Henry II the Pious, High Duke of Poland 1238–1241, had six toes on his left foot.{{cite book |publisher=Państwowe Zakłady Wydawn Szkolnych |last=Historyczne |first=Polskie Towarzystwo |title=Mowia, wieki: magazyn historyczny |language=pl |page=52 |url=https://books.google.com/books?id=mYYSAAAAIAAJ&q=Henryk+II+Pobo%C5%BCny+sze%C5%9B%C4%87+palc%C3%B3w |year=1961}}
• A boy named Hong Hong born in Pingjiang County, Hunan province, China, has 31 fingers and toes.{{cite web |url=http://www.ksl.com/?sid=39636334&nid=1313 |title=Chinese boy born with 31 fingers and toes |first=Jareen |last=Imam |work=CNN|date=May 4, 2016}}{{cite news |url=https://www.huffingtonpost.co.uk/entry/baby-hong-hong-31-fingers-toes_us_572ac6c2e4b0bc9cb045c0a4 |title= Baby Born With 31 Fingers And Toes In China |first=Dominique |last=Mosbergen |newspaper= Huffpost UK |date=May 5, 2016}}
• Kamani Hubbard, a boy in California, was born in 2009 with a rare case of polydactyly, with 12 fingers and 12 toes, all fully functional.{{cite news |url=https://abc7news.com/archive/6634255/#:~:text=Kamani%20Hubbard%20was%20born%20two,a%20condition%20known%20as%20polydactyly.&text=In%20fact%2C%20his%20parents%20say,few%20minutes%20after%20his%20birth. |title=Baby born with 12 fingers, 12 toes |publisher=ABC7 News |date=January 30, 2009 |location=Daly City, CA |access-date=July 17, 2020}}
• Johann Jacob Freiherr von Moscon (1621–1661), Lower Styrian baron, is depicted with six fingers at his left hand on a portrait from Brežice, Slovenia.{{citation needed|date=September 2018}}
• Jiang Qing, Mao Zedong's fourth wife, reportedly had six toes on her right foot.{{cite book |last=Li |first=Zhisui |title=The Private Life of Chairman Mao |publisher=Random House |year=1994 |isbn=978-0-679-76443-4 |url-access=registration |url=https://archive.org/details/privatelifeofcha00lizh_0}}
• Hrithik Roshan, a Bollywood actor born with a supernumerary thumb on his right hand.{{cite web |url=https://wiki.nus.edu.sg/display/HS/Famous+people+with+congenital+hand+anomalies |title=Famous people with congenital hand anomalies |last=Khor |first=Amy |date=February 2, 2019 |website=wiki.nus.edu|access-date=January 15, 2020}}
• Nayanthara, an Indian actress, has a rudimentary finger on her left hand.
• J. J. Weaver, an American college football outside linebacker, has six fingers on his right hand.{{cite web|url=https://theathletic.com/2889575/2021/10/15/kentuckys-win-over-florida-closed-a-chapter-for-jj-weaver-it-was-like-he-was-healed/|title=Kentucky's win over Florida 'closed a chapter' for J.J. Weaver: 'It was like he was healed'|first=Kyle|last=Tucker|website=The Athletic|date=October 15, 2021|access-date=July 25, 2024}}
• Akshat Saxena from Uttar Pradesh, India, is the world record holder for highest number of digits. He was born in 2010 with seven digits on each hand and 10 digits on each foot, for a total of 34 digits.{{cite news |url=http://www.cbsnews.com/news/akshat-saxena-sets-guinness-record-for-most-fingers-toes/ |title=Akshat Saxena sets Guinness record for most fingers, toes |author=David W. Freeman |website=CBS News |date=July 25, 2011 |access-date=February 13, 2016}}
• Garfield Sobers, West Indian cricketer, had an extra finger on each hand which he removed himself during childhood "with the aid of catgut and a sharp knife".{{cite book |last=Sobers |first=Garfield |author-link=Garfield Sobers |title=Garry Sobers: My Autobiography |publisher=Headline Book Publishing |date=May 1, 2002 |page=6 |isbn=978-0-7553-1006-7}}
• Theodore Roosevelt "Hound Dog" Taylor, Chicago-based American blues guitarist, was born with polydactyly on both hands, although around age 41, he removed the extra finger on his right hand.{{cite web |url=http://www.tdblues.com/2009/10/hound-dog-taylor-everyone-knows-the-hound/ |title=Hound Dog Taylor – Everyone Knows the Hound |website=TheDeltaBlues |url-status=dead |archive-url=https://web.archive.org/web/20131106040421/http://www.tdblues.com/2009/10/hound-dog-taylor-everyone-knows-the-hound/ |archive-date=November 6, 2013}}
• Varalakshmi V, a girl from Bangalore with eight fingers on each hand and about four to five extra toes on each foot.{{cite web |url=http://www.ndtv.com/article/cities/hope-for-bangalore-girl-with-27-fingers-and-toes-49433 |title=Hope for Bangalore girl with 27 fingers and toes |website=CitiesMid-Day.com |date=September 4, 2010}}
• Volcacius Sedigitus, a Roman poet of the 1st century, probably received his epithet, signifying "Sixfinger", because he was born with six fingers on each hand, according to Pliny.Natural History, by Pliny the Elder; volume 2, p.214.
• Zhu Yunming, a Chinese calligrapher, had six fingers on his right hand.{{citation needed|date=August 2020}}
• Reggy B, a drag queen and contestant on the second season of Drag Race Holland, revealed on the show that she was born with an extra thumb on her left hand, three extra toes on one foot, and two extra toes on her other foot. Her extra fingers and toes were surgically removed at a young age.

• In The Silence of the Lambs, Hannibal Lecter is described as having mid-ray duplication polydactyly (a duplicated middle finger) on his left hand, which he later removes in Hannibal as part of his cosmetic surgery to disguise himself.
• In the Disney XD 2012 cartoon series Gravity Falls, Stanford Pines ("Grunkle Ford") has six fingers on both of his hands, a trait which also identifies him in the show's mythology. He uses a tracing of his right hand to create the iconic gold detail on the covers of each of his journals.
• Tyrone Rugen, a Count in The Princess Bride, is described many times as "the six-fingered man".
• Void, an antagonist of the manga series Berserk, has six fingers on each hand.
• Zigzag, an antagonist from The Thief and the Cobbler, had six fingers on each hand.
• Billy, a character from Adventure Time, had six fingers on each hand.
• Kinzo Ushiromiya, the head of the Ushiromiya household from the visual novel Umineko When They Cry, had six toes on each foot. Among the many previous Ushiromiya family heads, those with polydactyly were known for their wisdom.
• In For Better or For Worse, Leah Nichols was born with 6 fingers on each hand.{{cite web |last1=Johnston |first1=Lynn |title=Wednesday, July 2, 1986 |url=https://fborfw.com/strip_fix/wednesday-july-2-1986/ |website=FBorFW Strip Fix |access-date=5 August 2023 |date=2 July 1986}}
• In Gattaca, Ryan Dorin plays a pianist with six fingers on each hand who throws his gloves to the audience at the concert's end.

File:Fig 5 29-11-2013-vereinfacht-deutsch.jpg population]]

Polydactyly occurs in numerous types of animals. The condition is sporadically seen in livestock, where it affects cattle, sheep, pigs, and occasionally horses.{{cite web|url=https://www.merckvetmanual.com/musculoskeletal-system/congenital-and-inherited-anomalies-of-the-musculoskeletal-system/congenital-and-inherited-anomalies-of-the-musculoskeletal-system-in-multiple-species|title=Congenital and Inherited Anomalies of the Musculoskeletal System in Multiple Species|last=Hanson, DMV|first=Russell |publisher= Merck Sharp & Dohme Corp.|archive-url=https://web.archive.org/web/20170731000507/https://www.merckvetmanual.com/musculoskeletal-system/congenital-and-inherited-anomalies-of-the-musculoskeletal-system/congenital-and-inherited-anomalies-of-the-musculoskeletal-system-in-multiple-species|access-date=8 April 2018|archive-date=2017-07-31}} Conversely, it is a common trait in several heritage chicken breeds. Chickens normally have 4 toes on each foot. The chicken breeds known for being polydactyl are the Dorking, Faverolle, Houdan, Lincolnshire Buff, Meusienne, Sultan, and non-bearded Silkie Bantams.{{cite web|url= https://extension.illinois.edu/eggs/res13-feet.html |title=Chicken Feet|author=|website=University of Illinois Extension: Incubation and Embryology|publisher=University of Illinois Board of Trustees |access-date=4 April 2017}}{{cite journal |last1=Corti |first1=Elio |last2=Moiseyeva |first2=Irina G |last3=Romanov |first3=Michael N |year=2010 |title=Five-toed chickens: their origin, genetics, geographical spreading and history |journal=Izvestiya of ТАА |issue=7 |pages=156–170 |s2cid=31294426 |url=http://www.summagallicana.it/Volume3/Five_toed_chickens_Izvestiya_2010.pdf }} The breed standard of these varieties of chickens calls for five toes on each foot, although sometimes more than five toes will occur. The extra digit in these breeds presents as an extra "thumb" that does not touch the ground. Mixed-breed chickens may also have extra digits if the aforementioned breeds are part of their genetic makeup.{{citation needed|date=October 2020}}

Polydactyly also occurs in dogs, cats, and small mammals such as guinea pigs{{cite web |url= http://animals.mom.me/polydactyly-guinea-pigs-6305.html|title=Polydactyly in Guinea Pigs|last=Kazmeyer|first=Milton |publisher=Whalerock Digital Media|archive-url=https://web.archive.org/web/20180409025611/http://animals.mom.me/polydactyly-guinea-pigs-6305.html|access-date=8 April 2018|archive-date=2018-04-09}} and mice.{{cite journal |last1=Fisher |first1=R. A. |title=Polydactyly in Mice |journal=Nature |date=March 1950 |volume=165 |issue=4193 |pages=407 |doi=10.1038/165407a0 |bibcode=1950Natur.165..407F |s2cid=4287187 |doi-access=free }} Cats normally have five digits on the front paws and four on the rear. Polydactyl cats have more, and this is a moderately common condition, especially in certain cat populations. Dogs, like other canids, normally have four claws on their rear paws; a fifth is often called a dewclaw and is especially found in certain dog breeds,{{cite journal | pmc = 2516088 | doi = 10.1534/genetics.108.087114 |date=Aug 2008 |author1=Park, K |author2=Kang, J |author3=Subedi, Kp |author4=Ha, Jh |author5=Park, C | title = Canine Polydactyl Mutations With Heterogeneous Origin in the Conserved Intronic Sequence of LMBR1 | volume = 179 | issue = 4 | pages = 2163–72 | pmid = 18689889 | journal = Genetics }} including the Norwegian Lundehund and Great Pyrenees.

A number of mutations of the LMBR1 gene, in dogs, humans, and mice, can cause polydactyly. A 2014 report indicated that mice could also exhibit polydactyly arising from mutation in the VPS25 gene.{{cite journal |last1=Handschuh |first1=Karen |last2=Feenstra |first2=Jennifer |last3=Koss |first3=Matthew |last4=Ferretti |first4=Elisabetta |last5=Risolino |first5=Maurizio |last6=Zewdu |first6=Rediet |last7=Sahai |first7=Michelle A. |last8=Bénazet |first8=Jean-Denis |last9=Peng |first9=Xiao P. |last10=Depew |first10=Michael J. |last11=Quintana |first11=Laura |last12=Sharpe |first12=James |last13=Wang |first13=Baolin |last14=Alcorn |first14=Heather |last15=Rivi |first15=Roberta |last16=Butcher |first16=Stephen |last17=Manak |first17=J. Robert |last18=Vaccari |first18=Thomas |last19=Weinstein |first19=Harel |last20=Anderson |first20=Kathryn V. |last21=Lacy |first21=Elizabeth |last22=Selleri |first22=Licia |title=ESCRT-II/Vps25 Constrains Digit Number by Endosome-Mediated Selective Modulation of FGF-SHH Signaling |journal=Cell Reports |date=October 2014 |volume=9 |issue=2 |pages=674–687 |doi=10.1016/j.celrep.2014.09.019 |pmid=25373905 |pmc=4223648 }} In cattle, it appears to be polygenic with a dominant gene at one locus and a homozygous recessive at another.

Polydactyly is believed to have been common in early tetrapods, particularly the extinct amphibians that represented the earliest landliving vertebrates. Their number of toes fluctuated until the early Carboniferous period when they finally began developing a uniform number of toes. Amniotes settled on five toes per limb, while amphibians developed four toes on each front limb and five toes on each back limb. (For more information, see Polydactyly in early tetrapods). Polydactyly also occurs in modern extant reptiles{{cite journal |last1=Bauer |first1=Aaron M. |last2=Hathaway |first2=Stacie A. |last3=Fisher |first3=Robert N. |title=Polydactyly in the Central Pacific Gecko, Lepidodactylus sp. (Squamata: Gekkonidae) |journal=Herpetology Notes |volume=2 |year=2009 |pages=243–246 |url=http://herpetologynotes.seh-herpetology.org/Volume2_PDFs/Bauer_Herpetology_Notes_Volume2_pages243-246.pdf |s2cid=85788238 |access-date=2018-04-09 |archive-date=2017-08-11 |archive-url=https://web.archive.org/web/20170811212035/http://herpetologynotes.seh-herpetology.org/Volume2_PDFs/Bauer_Herpetology_Notes_Volume2_pages243-246.pdf |url-status=dead }}

and amphibians.{{cite journal |last1=Cooper |first1=John E. |title=Some Albino Reptiles and Polydactylous Frogs |journal=Herpetologica |date=1958 |volume=14 |issue=1 |pages=54–56 |jstor=3890281 }} Polydactyly was a non-pathological, reacquired condition in extinct marine reptiles such as ichthyosaurs and hupehsuchians, some of which containing upwards of ten digits within their flippers.Sander, P.M. (2000). "Ichthyosauria: their diversity, distribution, and phylogeny". Paläontologische Zeitschrift. 74 (1–2): 1–35. {{doi|10.1007/bf02987949}}. S2CID 85352593.

File:The five toed cock of Aldrovandi.jpg|Rooster with feathered legs (Aldrovandi himself did not notice the five toes)Ornithologiae, Ulisse Aldrovandi (ill. Cristoforo Coriolano), 1599

File:The multiple toes of a polydactyl kitten.jpg|Kitten with 23 toes

File:Cairina moschata subspecies foot.jpg|Muscovy duck, both feet have five toes

File:Cairina moschata subspecies 0.jpg|Muscovy duck, both feet have five toes

{{reflist|32em}}

{{Medical resources

| DiseasesDB = 24853

| ICD10 = {{ICD10|Q|69||q|65}}

| ICD9 = {{ICD9|755.0}}

| ICDO =

| OMIM = 603596

| MedlinePlus = 003176

| eMedicineSubj = derm

| eMedicineTopic = 692

| MeshID = D017689

| SNOMED CT = 367506006

}}

{{commons category}}

{{Congenital malformations and deformations of musculoskeletal system }}

Category:Autosomal dominant disorders

Category:Congenital disorders of musculoskeletal system

Category:Fingers

Category:Supernumerary body parts