Polysyndactyly Explained

Field:Medical genetics

Polysyndactyly is a congenital anomaly, combining polydactyly and syndactyly, in which affected individuals have an extra finger or toe that is connected, via fusing or webbing, to an adjacent digit.[1] [2]

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Signs and symptoms

Presentations of polysyndactyly vary in location and size of the duplicated digit, and in the extent of webbing between digits.[3] [4]

The extra digit is most commonly postaxial,[5] 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.[6]

Polysyndactyly may be classified by the level of duplication. The extra digit may be small and comprise only soft tissue,[7] but usually includes at least one bone, most commonly the distal and middle phalanges.[4] [8] 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.

Causes

Polysyndactyly is typically inherited, in an autosomal dominant pattern.[9] 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[10] [11] [12] or the nearby pre-ZRS region.[13] [14]

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.[15] Patients with other syndromes, including Pallister-Hall syndrome[16] and Greig cephalopolysyndactyly syndrome[17] 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.[18]

Diagnosis

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.[19] Ultrasounds, typically done at the 14th to 16th week of pregnancy, can detect the presence of extra metacarpals, metatarsals, or phalanges.[20] 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.[21]

Treatment and Prognosis

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.[22] 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.[23]

External links

Notes and References

  1. Book: Lica L . Gale Encyclopedia of Medicine . Gale . 2020 . Longe JL . 6th . Polydactyly and Syndactyly.
  2. Book: Holmes LB . Common Malformations . October 2011 . Oxford University Press . 978-0-19-513602-9 . Limb Malformations . 146–205 . 10.1093/med/9780195136029.003.0015.
  3. Book: Stevenson RE . Human Malformations and Related Anomalies. . 2015 . Oxford University Press . Judith G. Hall, David B. Everman . 978-0-19-938604-8 . Cary . 936298415.
  4. Chen W, Chen L, Huang W, Tian X . Aesthetic and Anatomic Reconstruction of Polysyndactyly of the Fifth Toe Fused With the Fourth Toe . Annals of Plastic Surgery . 86 . 3 . 323–328 . March 2021 . 32568755 . 10.1097/SAP.0000000000002437 . 219982668 .
  5. Ko KR, Shim JS, Kang J, Park J . Surgical Outcomes and Predictive Factors of Medial Toe Excision for Polysyndactyly of the Fifth Toe . Foot & Ankle International . 42 . 5 . 562–569 . May 2021 . 33198478 . 10.1177/1071100720971289 . 226990510 .
  6. Dewan P, Agarwal N, Dewan P, Batta V . Familial crossed polysyndactyly in four generations of an Indian family . World Journal of Pediatrics . 6 . 2 . 177–180 . May 2010 . 20127219 . 10.1007/s12519-010-0020-7 . 11914996 .
  7. Woo SJ, Kim BJ, Kwon ST . Case-control study of the treatment of postaxial polysyndactyly of the foot: Comparison of surgical results after removal of the fifth or sixth toe . Archives of Plastic Surgery . 48 . 1 . 91–97 . January 2021 . 33503751 . 7861990 . 10.5999/aps.2020.01620 .
  8. Bae K, Kang MS, Kim TH, Park SS . Classification of Middle Phalangeal Postaxial Polysyndactyly Based on Intraoperative Arthrography Is Useful for Surgical Decision-making in Children Younger Than 2 Years . Journal of Pediatric Orthopedics . 41 . 7 . 437–443 . May 2021 . 33999568 . 10.1097/BPO.0000000000001858 . 234768434 .
  9. Saygin D, Tabib T, Bittar HE, Valenzi E, Sembrat J, Chan SY, Rojas M, Lafyatis R . 6 . Transcriptional profiling of lung cell populations in idiopathic pulmonary arterial hypertension . Pulmonary Circulation . 10 . 1 . 73–92 . March 1985 . 32166015 . 10.1111/j.1741-4520.1985.tb00636.x . 7052475 . free .
  10. Xu J, Wu J, Teng X, Cai L, Yuan H, Chen X, Hu M, Wang X, Jiang N, Chen H . 6 . Large duplication in LMBR1 gene in a large Chinese pedigree with triphalangeal thumb polysyndactyly syndrome . American Journal of Medical Genetics. Part A . 182 . 9 . 2117–2123 . September 2020 . 32662247 . 10.1002/ajmg.a.61757 . 220518629 .
  11. 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 . 6 . Microduplications encompassing the Sonic hedgehog limb enhancer ZRS are associated with Haas-type polysyndactyly and Laurin-Sandrow syndrome . Clinical Genetics . 86 . 4 . 318–325 . October 2014 . 24456159 . 10.1111/cge.12352 . 11858/00-001M-0000-0025-B3BA-6 . 27700015 . free .
  12. Dai L, Guo H, Meng H, Zhang K, Hu H, Yao H, Bai Y . Confirmation of genetic homogeneity of syndactyly type IV and triphalangeal thumb-polysyndactyly syndrome in a Chinese family and review of the literature . European Journal of Pediatrics . 172 . 11 . 1467–1473 . November 2013 . 23793141 . 10.1007/s00431-013-2071-y . 40376029 .
  13. 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 . 6 . A point mutation in the pre-ZRS disrupts sonic hedgehog expression in the limb bud and results in triphalangeal thumb-polysyndactyly syndrome . Genetics in Medicine . 20 . 11 . 1405–1413 . November 2018 . 29543231 . 10.1038/gim.2018.18 . free .
  14. 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 . 6 . The pZRS non-coding regulatory mutation resulting in triphalangeal thumb-polysyndactyly syndrome changes the pattern of local interactions . Molecular Genetics and Genomics . 297 . 5 . 1343–1352 . September 2022 . 35821352 . 10.1007/s00438-022-01921-2 . 250492417 .
  15. Temtamy SA . 1 July 1966 . Carpenter's syndrome: Acrocephalopolysyndactyly. An autosomal recessive syndrome . The Journal of Pediatrics . en . 69 . 1 . 111–120 . 10.1016/S0022-3476(66)80368-2. 5935752 .
  16. Consales A, Ardemani G, Cinnante CM, Catalano MR, Giavoli C, Villa R, Iascone M, Fontana C, Bedeschi MF, Fumagalli M . 6 . Neuroimaging appearance of hypothalamic hamartomas in monozygotic twins with Pallister-Hall syndrome: case report and review of the literature . BMC Neurology . 22 . 1 . 118 . March 2022 . 35331151 . 8943937 . 10.1186/s12883-022-02618-0 . free .
  17. Biesecker LG . The Greig cephalopolysyndactyly syndrome . Orphanet Journal of Rare Diseases . 3 . 1 . 10 . April 2008 . 18435847 . 2397380 . 10.1186/1750-1172-3-10 . free .
  18. Fried K, Mundel G . Polysyndactyly and Marfan's syndrome . Journal of Medical Genetics . 11 . 2 . 141–144 . June 1974 . 4366482 . 1013109 . 10.1136/jmg.11.2.141 .
  19. Zhang SJ, Lin HB, Jiang QX, He SZ, Lyu GR . Prenatal diagnosis of triphalangeal thumb-polysyndactyly syndrome by ultrasonography combined with genetic testing: A case report . World Journal of Clinical Cases . 9 . 23 . 6832–6838 . August 2021 . 34447832 . 8362503 . 10.12998/wjcc.v9.i23.6832 . free .
  20. Zimmer EZ, Bronshtein M . Fetal polydactyly diagnosis during early pregnancy: clinical applications . English . American Journal of Obstetrics and Gynecology . 183 . 3 . 755–758 . September 2000 . 10992205 . 10.1067/mob.2000.106974 .
  21. Book: Polysyndactyly . 2008 . Encyclopedia of Genetics, Genomics, Proteomics and Informatics . 1535 . Rédei GP . Dordrecht . Springer Netherlands . en . 10.1007/978-1-4020-6754-9_13251 . 978-1-4020-6754-9 . 239943368 .
  22. Burger E, 't Hart J, Hovius S, Van Nieuwenhoven C . Quality of life in children with preaxial polydactyly of the foot in comparison to adults, postaxial polydactyly and healthy controls . Journal of Pediatric Orthopedics. Part B . 31 . September 2022 . 1 . 27–33 . 36125884 . 10.1097/BPB.0000000000001004 . 252382615 .
  23. Gao Q, Wang S, Ren J, Wen X . Measuring parent proxy-reported quality of life of 11 rare diseases in children in Zhejiang, China . Health and Quality of Life Outcomes . 18 . 1 . 372 . November 2020 . 33225969 . 7682005 . 10.1186/s12955-020-01572-0 . free .

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