Polydactyly

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Polydactyly is a medical term used to describe extra fingers on the hands or toes on the feet[1]. They are a congenital anomaly as they are present at birth. The extras fingers and toes may vary in size as some are fully formed and functionally and others just small, non-functional nubs. Moreover, extra digits found adjacent to the thumb or big toes are known as pre-axial digits, while the ones located centrally in the hand or foot are known as post-axial digits [2]. In addition, polydactyly can occur bilaterally – both hands and feet, or it may occur on just one hand or foot and even a combination of both.

Inheritance

The probability of inheriting the condition varies as sometimes it appears to be a dominant trait with a 50% chance of being passed on to the gametes, whereas other times it appears recessive, giving a much lower chance of passing on the gene, depending on the partner’s history. In addition, the way in which the condition is expressed varies, for example, a parent might have an extra finger while their child has an extra toe. However, polydactyly can even occur when there is no family history of it.

Causes

Polydactyly occurs when the body follows a different set of directions than usual during the formation of the hands or feet in development, however researchers are still learning about the genes that cause the extra digit to form.

The trait may be passed down in families as an isolated, benign condition, like having a hitchhiker's thumb or being double jointed, which is considered a non-syndromic anomaly, otherwise, the trait may exist as part of a syndrome, which is a group of several recognizable clinical features that often occur together[3].

Some syndromes that might present with polydactyly include Asphyxiating thoracic dystrophy, Carpenter syndrome, Familial polydactyly and Trisomy 13 [4].

References

  1. Genome.gov, (2012). Polydactyly Study: General Information. [online] Available at: http://www.genome.gov/27529688 [Accessed 27 Nov. 2014].
  2. Genome.gov, (2012). Polydactyly Study: General Information. [online] Available at: http://www.genome.gov/27529688 [Accessed 27 Nov. 2014].
  3. Genome.gov, (2012). Polydactyly Study: General Information. [online] Available at: http://www.genome.gov/27529688 [Accessed 27 Nov. 2014].
  4. Nlm.nih.gov, (2014). Polydactyly: MedlinePlus Medical Encyclopedia. [online] Available at: http://www.nlm.nih.gov/medlineplus/ency/article/003176.htm [Accessed 27 Nov. 2014].

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