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Polydactyly is a condition in which a person has one or more extra fingers or toes and it can occur in one or both hands or feet. It is estimated that polydactyly occurs 1 in every 700-1,000 live births  . Polydactyly comes from the Greek words 'poly' meaning many and 'dactylus' meaning finger.
What Causes Polydactyly 
During the development of the embryo in the womb, the hand forms in the shape of a paddle and then in the sixth or seventh week of gestation, it splits into separate fingers. In rare cases, if there is a disruption in the process, an extra finger forms when a single finger splits into two.
The condition tends to run in families and it may also result from genetic mutations or environmental causes.
Types Of Polydactyly
1. Isolated polydactyly
It is passed on from the parent to a child through six genes, which are GLI3, GLI1, ZNF141, MIPOL1, PITX1, and IQCE. A mutation in one of these genes and their signalling pathways affects the growing limbs of the embryo during the first 4 weeks  .
Isolated polydactyly is divided into three categories:
- Postaxial polydactyly - It is the most common type of polydactyly. It develops as an extra finger on the outside of the hand or foot  .
- Preaxial polydactyly - The extra finger develops on the inside of the hand or foot, mostly on the thumb or big toe  .
- Central polydactyly - It is a rare type of polydactyly. The extra finger grows either beside the ring, middle, or index finger  .
2. Syndromic polydactyly
It is less common as compared to isolated polydactyly. A study showed that out of 5,927 people with polydactyly, only 14.6% of them had been born with an associated genetic disorder  .
There are many rare genetic syndromes linked to polydactyly, which include down syndrome, Greig syndrome, carpenter syndrome, triphalangeal thumb-polydactyly syndrome, syndactyly, acrocephalosyndactyly, Saethre-Chotzen syndrome, McKusick-Kaufman syndrome, Bardet-Beidl syndrome, short-rib polydactyly, and Pallister-Hall syndrome.
Symptoms Of Polydactyly
Extra fingers or toes that emerge on one or both of their hands or feet are either formed fully and functioning properlyor formed partially with some bones or just a small mass of soft tissue.
Diagnosis Of Polydactyly
Usually the diagnosis of polydactyly is done through ultrasound sonographs when the embryo is in the first three months of development  .
Treatment Of Polydactyly 
The treatment depends on which side the extra finger is developed.
Small finger duplication
The extra small finger doesn't require treatment and it doesn't affect your day-to-day activities. If the small finger doesn't contain any bones it can be removed easily, especially during birth. And if the small finger is fully formed, surgery is done to remove it.
Thumb finger duplication
It is difficult to remove an extra thumb because it can affect the functioning of the other thumb, which is why it isn't possible to remove the extra thumb. However, there are different surgical options available depending on the position and formation of the extra thumb.
Central fingers and toes
The surgical options are as follows:
- Removing the extra central finger and rebuilding the finger it is attached to
- Removing both fingers and rebuilding one new finger
- Keeping the extra central finger, but the tendons and ligaments are operated to avoid deformities
In most cases, the extra finger is removed when the child is in its first two years.
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