There are three main causes of hemifacial microsomia:

Autosomal Dominant

Autosomal dominant means that one gene is needed to cause the condition. The gene is passed from parent to child with a 50% risk for each pregnancy. Males and females are equally impacted. The condition does not impact the parent and child the same. A parent may have a very mild sign of hemifacial microsomia, such as a skin tag by the ear, but the child has a more serious case.

Autosomal Recessive

Autosomal recessive means that two copies of the gene are needed to cause the condition, one from each parent. Parents have a 25% chance with each pregnancy to have a child with hemifacial microsomia. Males and females are equally impacted.

Multifactorial

Multifactorial inheritance means that "many factors" cause the defect. The factors are normally both genetic and environmental. Males are slightly more likely to be affected than females.

The deformity in hemifacial microsomia can be mild or serious. It can impact many different parts of the face. In the more severe cases, the following structures are not fully formed:

• The external and middle ear
• The side of the skull
• The thickness of the cheek tissue
• The upper and lower jaws
• The teeth
• Some of the nerves that allow facial movement

In the milder forms, only some of the structures are affected and not as seriously.

Specific treatment for HFM depends on the specific types of HFM. Any child with suspected HFM should be evaluated by a craniofacial anomalies team. Each of the specialists will have a proposed treatment plan depending on the severity of your child's specific case.

After examining your child and meeting with a craniofacial team, the following treatment options may be discussed:

• For severe underdevelopment of the lower jaw, reconstruction using a bone graft taken from the ribs.
• Another possibility to lengthen the underdeveloped jaw is to place a device on the jaw for bone distraction. This technique avoids the need for bone grafts.
• The external ear is usually reconstructed between the ages of 6 to 8. This takes multiple surgeries with several months between.
• Additional surgery in the soft tissue of the cheek to make them more symmetrical or possibly jaw surgery may be needed when your child becomes a teenager.