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Preaxial Polydactyly Type 2 and Associated Limb Defects 

Preaxial Polydactyly Type 2 and Associated Limb Defects
Preaxial Polydactyly Type 2 and Associated Limb Defects

Robert Hill

and Laura Lettice

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date: 28 February 2021

Sonic hedgehog (SHH) gene regulates the pattern and the number of fingers and toes that form during embryonic development of the limb. Genetic mutations occur that affect this process leading to congenital limb defects. Analysis of the genetic mechanism shows that the mutations effect regulatory changes in the limb specific enhancer of the SHH gene. This enhancer, called the ZRS, lies within an intron of the LMBR1 gene and acts at a long distance over a gene desert to control the expression of SHH. Both single base pair mutations within the ZRS and chromosomal microduplications that give rise to tandem copies of the ZRS cause misexpression of SHH in the limb. The misexpression is responsible for a spectrum of defects in the limb including preaxial polydactyly, syndactyly and tibial hypoplasia.

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