What causes Microtia:

At the current time, no specific gene has been identified that causes this condition, and almost never does someone with hemifacial microsomia pass the trait on to his or her children (less that 5% chance). The exact cause of this condition remains unknown but there is some experimental evidence, published many years ago, that suggested if a small blood vessel ruptures near the developing ear in mice before they are born (so this area ends up getting less blood), after birth the mice will have an absent ear. More likely, this condition results from an impaired flow of cells (called neural crest cells), which arise adjacent to the spinal cord and travel to the face to form the facial skeleton. We know that if not enough of these cells are able to successfully migrate to their intended location, the ear is either smaller, or absent. It has been suggested that some medications may lead to this condition, but this is extremely hard to prove. In conclusion, all current evidence suggests that many complicated factors lead to microtia, and there is nothing that the mother did wrong during pregnancy to cause this to happen.

Can my child hear out of this ear? | Treatment
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