| Polydactyly | |
|---|---|
| Classification and external resources | |
27 year old male with unilateral polydactyly affecting the left thumb. The supernumerary digit had normal sensation but no joint and hence could not move independently |
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| ICD-10 | Q69 |
| ICD-9 | 755.0 |
| OMIM | 603596 |
| DiseasesDB | 24853 |
| eMedicine | derm/692 |
| MeSH | D017689 |
Polydactyly or polydactylism (from Ancient Greek πολύς (polus) "many" + δάκτυλος (daktulos) "finger"), also known as hyperdactyly, is a congenital physical anomaly in humans, dogs, and cats having supernumerary fingers or toes.[1]
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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.[2]. The world record holder for highest number of digits is Akshat Saxena from Uttar Pradesh, India. He was born in 2010 with 7 digits on each hand and 10 digits on each foot, for a total of 34 digits.[3]
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.[4] 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.
Types include:
| OMIM | Type | Locus |
|---|---|---|
| 174200 | Postaxial A1 | GLI3 at 7p13 |
| 602085 | Postaxial A2 | 13q21-q32 |
| 607324 | Postaxial A3 | 19p13.2-p13.1 |
| 608562 | Postaxial A4 | 7q22 |
| 174400 | Preaxial I | ? |
| 174500 | Preaxial II | SHH at 7q36 |
| 174600 | Preaxial III | ? |
| 174700 | Preaxial IV | GLI3 at 7p13 |
Syndromes including polydactyly include Acrocallosal syndrome, Basal cell nevus syndrome, Bardet-Biedl syndrome, Biemond syndrome, Ectrodactyly-ectodermal dysplasias-cleft lip/palate syndrome, Ellis van Creveld syndrome, Meckel Gruber syndrome, McKusick-Kaufman syndrome, Mirror hand deformity, Mohr syndrome, Oral-facial-digital syndrome, Pallister-Hall syndrome, Rubinstein-Taybi syndrome, Short rib polydactyly, and VATER association.[5] It can also occur with a triphalangeal thumb.
The condition has an incidence of 1 in every 500 live births.[6] 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.[7] 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.[8]
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.
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.[16] 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,[16] including the Norwegian Lundehund and Great Pyrenees.
Polydactyly was common in the earliest tetrapods, the number of digits settling to the common five on each foot in amniotes and four to the hand and five to the foot in amphibians in the early Carboniferous, see Polydactyly in early tetrapods
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