Syndactyly FAQ: How is Syndactyly Inherited and What are the Causes of Syndactyly?

Syndactyly FAQ:  How is Syndactyly Inherited and What are the Causes of Syndactyly?
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What is Syndactyly?

Syndactyly is a congenital abnormality where two or more fingers or toes are fused together. There are varying degrees of severity which can include the skin between the affected digits being partially fused (incomplete syndactyly) or fully fused (complex syndactyly). In some instances the bones and sometimes the nails are fused together (complex syndactyly).

Syndactyly is a cosmetic condition in that it does not affect any abilities such as walking, running, or handling objects. There is no evidence to suggest that having fully or partially webbed toes affects swimming ability.

Syndactyly occurs on its own as an isolated condition or as a feature of several other conditions, including Apert syndrome and Holt-Oram syndrome.

What are the Causes of Syndactyly?

The cause of syndactyly is a failure of the skin and/or bones between digits to separate during development, and the molecular blame for this is sometimes laid at the door of a protein called sentrin which determines when cells die. During embryonic development this usually ensures that there isn’t any unusual skin growth between digits. However, if there is a faulty sentrin protein then programmed cell death fails, and webbed fingers or toes can result. In many cases gene mutations are to blame for the faulty protein. Other genes have also been heavily implicated in the causes of syndactyly.

However, it is also likely that in some instances there are environmental causes for webbed toes or feet, and these might be environmental toxins and pollutants, or abnormalities in the womb.

How is Syndactyly Inherited?

Syndactyly as far is as is known follows an autosomal dominant pattern of inheritance. This means that, first of all, it is not a sex-linked condition, so males and females are equally likely to inherit the condition, and secondly that children who have one parent with syndactyly have a 50% chance of inheriting the abnormality.

What are the Genetics of Syndactyly?

Several candidate genes and chromosomal regions have been discovered that may contribute to the various types of syndactyly. There is so much that is unknown, including the number and types of genes, and the nature of the mutations that cause syndactyly, or how those mutations cause the abnormality.

  • Syndactyly type 1 is the most common type of isolated syndactyly, and there is complete or partial webbing between the third and fourth fingers and/or the second and third toes. A region on chromosome two that is near to the HOXD cluster has been identified as containing a possible candidate gene.

  • Syndactyly type 2 where webbing can occur between the third and fourth fingers, and there may be an additional digit, can be caused by mutations in the HOX 13 gene on chromosome two. Hox genes are the pattern formation genes that are involved in controlling how body patterns are laid down and ensuring that our body parts such as limbs are in the correct place.

There are numerous genes involved in limb formation and they encode proteins such as fibroblast growth factors and bone morphogenic proteins, and candidate genes may exist here.

Who are Some Famous People with Syndactyly?

Hollywood A-lister and renowned tweeter Ashton Kutcher - has revealed his slightly webbed toes to chat show hosts, including Jonathon Ross in the UK.

Comic actor Dan Aykroyd - claims he has webbd toes

UK popstar and celebrity Rachel Stevens - has webbed toes

Photo Credit

Released into the public domain by Dumplestilskin