Polydactyly

from Wikipedia, the free encyclopedia
Classification according to ICD-10
Q69 Polydactyly
Q69.0 Accessory finger (s)
Q69.1 Accessory thumb (s)
Q69.2 Accessory toe (s)
Accessory big toe
Q69.9 Polydactyly, unspecified
Excess finger (s) or toe (s) not specified
ICD-10 online (WHO version 2019)
Fig. 1 Left hand with six fully developed fingers (postaxial)
Fig. 2 Right foot with bifurcative, incompletely formed 6th toe (postaxial)
Fig. 3 Left hand of a 27-year-old man with unilateral, preaxial polydactyly on the thumb. The additional finger shown is normally sensitive, but has no joint of its own and can therefore not be moved independently of the thumb.

The polydactyly (from Greek πολύς polys , much 'and δάκτυλος daktylos , finger', so literally "Vielfingerigkeit") refers to a hereditary, congenital anatomical specificity with regard to the number of additional manual and / or Fußgliedmaßen. The peculiarity can occur in humans, but also in cats, dogs, birds, guinea pigs and other animals. People with polydactyly have more than the usual number of fingers or toes. It is particularly common to find a sixth finger on one or both sides (usually an incomplete double thumb ) or double big toe ( hexadactyly ). Polydactyly is usually inherited as an autosomal dominant trait.

In addition to the isolated form, polydactyly occurs as a symptom in more than 90 different syndromes , e.g. B. in the Pätau syndrome (trisomy 13), the Edwards syndrome (trisomy 18), the C syndrome , the Ellis-van-Creveld syndrome , the Laurence-Moon-Bardet-Biedl syndrome , the Meckel-Gruber -Syndrome and the forms of short-rib polydactyly syndromes (types I, II, III, IV). In the total incidence of polydactyly cases, however, syndromes are not represented at around 15%.

classification

The polydactyls can be classified according to localization into:

  • Preaxial on the side of the 1st ray
  • Axially or centrally on the II.-IV. Beam
  • Postaxial on the side of the fifth ray

Epidemiology

Isolated polydactyly - the most common variant is hexadactyly - has a frequency of 1: 3,000 in humans in Europe, Asia and North America, and 1: 300 in Africa. In about 40 percent of the cases, the change occurs on both sides. Polydactyly is generally reported with a frequency of 1: 500 live births. Postaxial polydactyly of the hand is a common malformation among black children in Africa. An autosomal dominant inheritance is assumed here. Postaxial polydactyly is more common in blacks than whites and more common in males. In comparison, postaxial polydactyly typically forms syndromes in white children and is associated with an autosomal recessive inheritance. A 2008 study combined data from Jefferson County Alabama , USA, and Uppsala , Sweden. This study gives the frequency of all summarized polydactyly forms with 2.3 per 1000 male white, 0.6 per 1000 female white, 13.5 per 1000 male black and 11.1 per 1000 female black live births. The most extensive empirical study on polydactyly to date was published in 1996. 6912 cases of polydactyly were analyzed and classified from a total of four million births in Spain and South America.

Polydactyly forms

The most common differentiation is preaxial polydactyly (thumb side, Figs. 3, 6, 7, 9), postaxial polydactyly (outside of hand, Fig. 1, 2, 4) and (rarely) central polydactyly on the ring, middle or rather on the index finger. Central polydactyly is often associated with syndactyly . The combination becomes polysyndactyly . Other malformations of the fingers and toes are dysmelia , brachydactyly, and oligodactyly .

The currently known maximum is a Chinese boy with 15 fingers and 16 toes. His mother has 12 fingers and 12 toes each. This corresponds to a maximum of 3 additional limbs per limb.

Additional fingers and toes can be surgically removed through amputation procedures. Surgery is often performed for aesthetic reasons. Operations can also serve to improve the ability of those affected to reach and walk.

Fig. 4 Postaxial polydactyly of the right hand in a 10-year-old girl

Polydactyly in animals

Fig. 5 Acanthostega , early terrestrial vertebrate. Foot with 8 toes. Some of these have no identity of their own, which is why polydactyly is assumed.

Cats typically have five toes on the forefoot and four toes on the hind foot, 18 toes total. A cat with an extra toe on two or more paws is also known as a ship's cat . The polydactyl cat breeds include the Maine Coon , which develops a special form of preaxial polydactyly, the Hemingway mutants, so named because Ernest Hemingway had a population of such cats in his house in Key West, Florida. Another breed of cat with polydactyly is the pixiebob . In contrast to the Maine Coon, the feature of extra toes is permitted in breeding standards in the Pixiebob. A number of mutations in the LMBR1 gene can cause polydactyly in dogs, humans, and mice. In the wild type, like other canines, dogs have four toes on their hind feet. A fifth, wolf's claw , occurs in some breeds. Polydactyly is known in the Norwegian Lundehund and the Pyrenees Dog ( Chien de Montagne des Pyrénées ). The Norwegian Lundehund is the only four-footed vertebrate ( tetrapod ) that is defined as the standard with at least six toes on each foot and thus occurs predominantly with these features, but also with even more toes. Polydactyly is also a common trait in some chicken breeds, including the silkie, and in pigs (Fig. 9). A comprehensive early study of polydactyly in an inbred guinea pig strain was made by the evolutionist Sewall Wright (1934). The British evolutionary researcher William Bateson undertook extensive polydactyly studies as early as 1894 with precise anatomical analyzes of humans, macaques, cats, horses ( atavism ), calves and other species. The studies should help to support Bateson's criticism of Darwin's theory of evolution, according to which gradual evolutionary steps do not dominate, but evolutionary change predominates in larger, discontinuous steps. Today we know that both occur.

Polydactyly is also assumed in early Devonian tetrapods such as Ichthyostega , Acanthostega or Tulerpeton , even if the possibility cannot be ruled out that the Ichthyostega wild type normally had more than five toes per limb. Based on the forefeet of Pederpes , a post-Devonian tetrapod from the Tournaisium with five big toes and one small rudimentary toe, Jennifer Clack assumes that pentadactyly began as a functional condition during this period and subsequently became an anatomical fixation led. Ultimately, it is not scientifically clarified today through which selection conditions the very robust pentadactyly evolved in large areas of the tetrapods. Only one species of amphibian, a particular clawed frog , is known to show signs of six regular toes in the animal kingdom today. Other species such as the panda bear , certain mole species or the elephant did not evolve a real additional toe, but usually an extension of a metatarsal bone ( sesamoid bone ).

Genetic causes

Fig. 6 Preaxial polydactyly: Additional ectopic Shh expression on the later side of the thumb (arrow). Here analogy of the Hemingway mutant in the mouse.
Fig. 7 Preaxial polydactyly: Maine Coon cat, Hemingway mutant (right forefoot)
Fig. 8 Preaxial polydactyly, Hemingway mutant: frequency of polydactyl toe numbers per individual: statistically skewed distribution

Polydactyly has been linked to several mutations. As a rule, these are not gene mutations themselves, but mutations in a cis element that is responsible for controlling the expression of a particular gene. The Sonic Hedgehog (SHH) signal transduction pathway is often affected , less often the Indian Hedgehog signal pathway (Double foot Mutant) or the BMP signal pathway . Furthermore, mutations in the Hoxa and Hoxd clusters are described which lead to polydactyly. Interaction of Hoxd13 with Gli3 induces synpolydactyly, a combination of additional fingers or toes that have grown together. Other important signaling pathways in this context are fibroblast growth factors (FGF), the Wnt signaling pathway and the Notch signaling pathway .

In a special case of preaxial polydactyly in cats (Hemingway mutant) (Figs. 6 and 7) there is a mutation of the cis regulatory element ZRS (ZPA regulatory sequence), a non-coding region about 800,000 base pairs away from the target gene Shh. As a result, in addition to normal expression, there is also ectopic expression of Shh on the anterior (front) side of the extremity bud (Fig. 6). Normally Shh is expressed in a certain organizing region, the zone of polarizing activity (ZPA) on the outside of the bud ( posterior , back) and the control molecules that arise there diffuse from there in an anterior direction (forwards) across the direction of growth of the extremity. The mutation, on the other hand, leads to an additional mirror-image, albeit smaller, ectopic formation of a new organizing region on the anterior palm. This stimulates additional cell growth (proliferation) there and thus provides the raw material for one or more new preaxial fingers or toes.

In addition to studying the genetic causes of polydactyly, pattern formation models of the hand are used to simulate malformations in the computer at the cellular level and in this way to explain the development process more clearly (see: Extremity Development ).

Example of polyphenism

Polydactyly is the result of a genetic point mutation , mostly in Sonic Hedgehog , GLI3, or BMP . The mutations lead to a number of different forms of variation. An example of this are the Hemingway mutants mentioned in cats. Since here an identical error in the DNA spontaneously (without known or assumed environmental influences) leads to various preaxial malformations with different numbers of fingers or toes, this is a special case of polyphenism .

A more recent study of the polydactyl toe numbers of 375 Hemingway mutants showed that, firstly, the number of additional toes was variable ( plastic ) and, secondly, the number of additional toes - statistically speaking - was not evenly distributed (Fig. 8). The Maine Coon cat (as the basic model of the Hemingway mutants) has 18 toes as wild type. In some cases, polydactyly occurred with an unchanged number of toes (18 toes), the difference being that the extension of the first toe resulted in a three-jointed thumb. However, 20 toes were found much more frequently and, with decreasing frequency, 22, 24 or 26 toes (Fig. 8). There were also, but less often, odd total numbers of toes on the feet. There was also a statistical skew of the distribution in the difference in the number of toes on the front and rear feet. In addition, a left-right asymmetry in the number of toes could be observed. Based on model calculations, the authors of the study suggested that random bistabilities during the development process could explain the observed statistical skewness of the distribution.

Consequences for the theory of evolution

Fig. 9 Polydactyly on the forefoot of a domestic pig (Prentiss 1903)

While in biology and medicine polydactyly is considered to be a pathological undesirable development, many of its phenomena open up from the point of view of evolutionary developmental biology an expanded view of how innovations can arise in evolution, namely in terms of development within a generation and inherited. Since polydactyl fingers or toes do not have a homologous feature, i.e. since there are neither cells nor tissue in the place of a new finger in the wild type , a polydactyl finger or toe can - technically speaking - also be viewed as a complete phenotypic innovation.

The way in which new toes were created in Hemingway mutants can therefore be seen as an example of how in other cases evolutionary new elements arise that are not only homologous to the previous generation but also to the same organism.

As an evolutionary variation , polydactyly cannot be explained with Darwin's theory of evolution , nor with the synthetic theory of evolution . Only the Advanced synthesis in evolutionary theory this can be found EvoDevo mechanisms that describe is generated as the phenotype in development.

History of science of polydactyly

Early scientific research into polydactyly goes back to the French Pierre-Louis Moreau de Maupertuis (1751), Charles Darwin (1868) and the British William Bateson (1894). In the course of the history of science, different priorities in polydactyly research become clear. These range from hereditary rules to evolutionary significance, exact anatomical analyzes to research into molecular causes and, more recently, increasingly the development of extremities. The analysis of the variation in toe numbers and the genotype-phenotype relationship are also moving back into the focus of research.

Fine arts and literature

In the fine arts there are numerous depictions of people or gods with six fingers or toes, including: frescoes in Portugal, statues in Australia, Polynesia, South America, Mexico, reliefs in Egypt and medieval panel paintings in Europe. The oldest textual mention of a hexadactyly can be found in the Old Testament, 2 Samuel 21:20  ELB : “And again there was a fight at Gath. There was a long man who had six fingers on his hands and six toes on his feet, 24 in number […]. ”In the Gothic pilgrimage church in Maria Laach am Jauerling , Austria , a miraculous image of St. Mary adored with six fingers. In the painting “The Marriage of the Virgin” 1504, Raphael represents St. Joseph with six toes. Also with St. Sixtus in Raphael's painting Sistine Madonna (1512–1513) some viewers see six fingers (the little “finger” at the bottom, however, is part of the palm). In his novel Chicken Christl , published in 2004, the Austrian author Martin Amanshauser portrays the first-person narrator Mika as a hexadactyl. Marion Zimmer Bradley's Darkover series (1958–2013) portrays the six-fingered indigenous race of the Chieri. Individuals with mixed human and Chieri parents and their descendants (some of whom inherit the six-fingered hands of their forefathers) constitute a significant proportion of the main characters portrayed in the series.


In the Hollywood film Gattaca , which deals with genetic optimization in the form of a dystopia, there are pianists with twelve fingers who alone are able to play specially composed pieces for twelve fingers.

Affected

The cartoonist Uderzo (1927-2020) was born with two sixth fingers that were surgically removed.

See also

literature

Web links

Commons : Polydactyly  - Collection of images, videos, and audio files

Individual evidence

  1. ^ Wilhelm Gemoll : Greek-German school and hand dictionary . G. Freytag Verlag / Hölder-Pichler-Tempsky, Munich / Vienna 1965.
  2. ↑ Polydactyl Cats (Part 1). Retrieved January 20, 2007 .
  3. ↑ a b c K. Park, J. Kang, KP Subedi, JH Ha, C. Park: Canine polydactyl mutations with heterogeneous origin in the conserved intronic sequence of LMBR1. In: Genetics . tape 179 , no. 4 , August 2008, ISSN  0016-6731 , p. 2163-2172 , doi : 10.1534 / genetics.108.087114 , PMID 18689889 , PMC 2516088 (free full text).
  4. ^ Warren DC 1949. Linkage relations of autosomal factors in the fowl. Genetics 34: 333-350.
  5. ^ Wright p. 1934. An analysis of variability in number of digits in an inbred strain of guinea pigs. Genetics 19: 506-536.
  6. ↑ Castilla EE, Lugarinho R., da Graça Dutra M., Salgado LJ 1998. Associated anomalies in individu- als with polydactyly. American Journal of Medical Genetics 80: 459-465.
  7. ↑ F. Hefti: Pediatric Orthopedics in Practice . Springer, 1998, ISBN 3-540-61480-X , p. 396.
  8. ↑ a b c Wolfgang Regal, Michael Nanut: One too many (Narrenturm 129). In: Doctors Week. Edition 6/2008 from February 8, 2008. Online ( Memento from December 24, 2013 in the Internet Archive )
  9. ^ Khanh-Van Le-Bucklin, Rebecca Hicks, Alan Greene: Polydactylism. Dr. Greene, July 30, 2008; accessed February 9, 2010 .
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  11. ↑ Denise M. McCarthy, Carter G. Abel: Supernumerary Digit. eMedicine, July 31, 2008, accessed February 9, 2010 .
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  13. ↑ Polydactyly in Pictures: Chinese Baby Born With 15 Fingers and 16 Toes ( Memento from February 17, 2017 in the Internet Archive ) /
  14. ^ Dally Mail May 2, 2016
  15. ↑ Carlene Fredericka Brennen: Hemingway's Cats. An Illustrated Biography. Pineapple Press. Sarasota Florida, USA 2006.
  16. ^ CW Prentiss: Polydactylism in man an the domestic animals with especial reference to digital variations in swine. Cambridge Mass. 1903.
  17. ^ S. Wright: An Analysis of Variability in Number of Digits in an Inbred Stain of Guinea Pigs. In: Genetics. 19 (6), 1934, pp. 506-536.
  18. ^ William Bateson: Materials of the study of variation: Treated with especial regards to discontinuity in The origin of species (1894). MacMillan & Co, London.
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  21. ↑ Hayashi S., Kobayashi T., Yano T., Kamiyama N., Egawa S., Seki R., Takizawa K., Okabe M., Yokoyama H., Tamura K. 2015. Evidence for an amphibian sixth digit. Zoological Letters 1:17.
  22. ↑ Why animals step out of line with six fingers N24 September 24, 2011
  23. ↑ The elephant has a kind of sixth toe. Deutschlandfunk December 23, 2011
  24. ^ RE Hill: How to make a zone of polarizing activity: insights into limb development via the abnormality preaxial polydactyly. In: Development, growth & differentiation. Volume 49, Number 6, August 2007, ISSN  0012-1592 , pp. 439-448, doi: 10.1111 / j.1440-169X.2007.00943.x , PMID 17661738 (review).
  25. ^ RE Hill, LA Lettice: Alterations to the remote control of Shh gene expression cause congenital abnormalities. In: Philosophical transactions of the Royal Society of London. Series B, Biological sciences. Volume 368, number 1620, 2013, ISSN  1471-2970 , p. 20120357, doi: 10.1098 / rstb.2012.0357 , PMID 23650631 , PMC 3682722 (free full text).
  26. ^ LG Biesecker: Polydactyly: how many disorders and how many genes? 2010 update. In: Developmental Dynamics . Volume 240, number 5, May 2011, ISSN  1097-0177 , pp. 931-942, doi: 10.1002 / dvdy.22609 , PMID 21445961 , PMC 3088011 (free full text) (review).
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  28. ↑ a b L. A. Lettice, AE Hill, PS Devenney, RE Hill: Point mutations in a distant sonic hedgehog cis-regulator generate a variable regulatory output responsible for preaxial polydactyly. In: Human Molecular Genetics. 17 (7), (2008), pp. 978-985.
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  30. ↑ a b c Axel Lange, Hans L. Nemeschkal, Gerd B. Müller : Biased polyphenism in polydactylous cats carrying a single point mutation: The Hemingway Model for digit novelty. In: Evolutionary Biology. Dec. 2013.
  31. ^ GB Müller: Epigenetic Innovation. In: Massimo Pigliucci, Gerd B. Müller (Ed.): Evolution - The Extended Synthesis. MIT Press, 2010, p. 311.
  32. ^ Image of grace Maria six fingers in Maria Laach
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  34. ↑ Hans Gross. In: Contributions to the psychology of the statement. 1904, pp. 249-254. Google books
  35. ↑ amanshauser.at
  36. ↑ series Chronologically the first occurrence of Chieri in Darkover Landfall , Marion Zimmer Bradley, DAW Books ., 1972
  37. ↑ ORF at / Agencies red: 1927–2020: Asterix artist Uderzo is dead. March 24, 2020, accessed on March 25, 2020 .