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Polydactyly
Classification and external resources
Bilateral polydactyly with short fingers in an Ellis-van Creveld syndrome patient.
ICD-10	Q69.
ICD-9	755.0
OMIM	603598
DiseasesDB	24853
eMedicine	derm/692

Polydactyly or polydactylism (from Ancient Greek πολύς (polus) "many" + δάκτυλος (daktulos) "finger"), also known as hyperdactyly, is a congenital physical anomaly in humans having supernumerary fingers or toes. When each hand or foot has six digits, it is sometimes called sexdactyly, hexadactyly, or hexadactylism.

The extra digit is usually a small piece of soft tissue; 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.^[1]

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.^[2] 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.

The condition has an incidence of 1 in every 500 live births.^[3] Postaxial hand polydactyly is a common isolated disorder in African black and African American children, and autosomal dominant transmission is suspected. Postaxial polydactyly is approximately 10 times more frequent in blacks than in whites and is more frequent in male children.^[4] In contrast, postaxial polydactyly seen in white children is usually syndromic and associated with an autosomal recessive transmission. One study by Finley et al. combined data from Jefferson County, Alabama, United States and Uppsala County, Sweden. This study showed incidence of all types of polydactyly to be 2.3 per 1000 in white males, 0.6 per 1000 in white females, 13.5 per 1000 in black males, and 11.1 per 1000 in black females.^[5]

Left foot with postaxial polydactyly of 5th ray

Right hand with mid-ray duplication

[edit] In various species

Cats normally have five digits on the front feet and four on the rear. Polydactyl cats have more, and this is a moderately common condition, especially in certain cat populations.

Polydactyly is a common trait in several heritage chicken breeds, including silkies.

A number of mutations of the LMBR1 gene, in dogs, humans, and mice, can cause polydactyly.^[6] 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,^[6] including the Norwegian Lundehund and Great Pyrenees.

[edit] Real human polydactyls

• Hrithik Roshan, a Bollywood actor born with a supernumerary thumb on his right hand.^[7]
• Antonio Alfonseca, a Major League Baseball pitcher.
• Hampton Hawes, jazz pianist, was born with six fingers on each hand (surgically removed shortly after birth)^[8]
• Little Tich, an English music hall comedian.
• 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".^[9]
• Gemma Arterton,^{[10] [11]} actress.
• Toyotomi Hideyoshi, Japanese daimyo who unified Japan in the Sengoku period.
• Sid Wilson, turntablist of Slipknot. He was born with an extra digit on his hands and feet. They were dead, however, and were removed shortly after birth.
• Blues guitarist Hound Dog Taylor[2]
• Roman era poet Volcatius Sedigitus.
• Kamani Hubbard, a boy born with a rare case of polydactyly with 12 fully functioning fingers.

[edit] References

1. ^ http://www.eatonhand.com/hw/hw024.htm
2. ^ Polydactyly and Syndactyly
3. ^ Polydactylism FAQ
4. ^ http://www.pennmedicine.org/encyclopedia/em_displayArticle.aspx?gcid=003176&ptid=1
5. ^ [1]
6. ^ ^{a b} Park, K; Kang, J; Subedi, Kp; Ha, Jh; Park, C (Aug 2008). "Canine polydactyl mutations with heterogeneous origin in the conserved intronic sequence of LMBR1." (Free full text). Genetics 179 (4): 2163–72. doi:10.1534/genetics.108.087114. ISSN 0016-6731. PMID 18689889. PMC 2516088. http://www.genetics.org/cgi/pmidlookup?view=long&pmid=18689889. 
7. ^ Hrithik Roshan Factfile
8. ^ JazzScript
9. ^ Gary Sobers, My Autobiography, Headline, 2003, p.6.
10. ^ Arterton's Extra Digits
11. ^ Parade (magazine); 11 October 2009, page 2.