I believe symbrachydactyly occurs due to difficulties with the AER and the underlying mesoderm during development- please see previous description of limb development http://congenitalhand.wustl.edu/2012/10/limb-formation.html If the AER is lost, limb outgrowth stops and there is a deficient limb. The theory is that early loss (i.e., at 4-5 weeks of gestation) leads to a really short limb and later loss (i.e., at 6-7 weeks of gestation) leads to more subtle symbrachydactyly. The following children would be considered to have a severe symbrachyactyly- at least the way I consider it. We have shared our thoughts and experiences with this diagnosis in the Journal of Hand Surgery: http://www.ncbi.nlm.nih.gov/pubmed/17996776
|Nubbins of symbrachydactyly|
|Another example of severe symbrachydactyly|
Others believe severe symbrachydactyly really should be called a transverse arrest or congenital amputation of the limb. I don't mind those terms but I happen to believe this is most likely a development issue (a malformation)- meaning that something went wrong during limb development, not after.
The above examples differ from less severe symbrachydactyly:
|Short finger type of symbrachydactyly- short, webbed fingers.|
|Another short finger symbrachydactyly|