Hemifacial microsomia is a general diagnosis used to describe facial birth defects of varying severity that may involve certain differences in the eyes, ears, facial bones, mouth, neck, or spine. These defects usually affect only one side of the face, with that side of the face appearing smaller than the other side.
Individuals with hemifacial microsomia have physical differences that are present at birth (congenital). These abnormalities are typically limited to the head and bones of the spinal column (vertebrae) and may be severe or mild. In some cases, the changes are seen on both sides of the face (bilateral). In other cases, they are limited to one side of the face (unilateral).
Different terms may be used for this pattern of differences. Hemifacial microsomia may also be called Goldenhar syndrome, facioauriculovertebral sequence, or oculoauriculovertebral spectrum. This final name describes the common birth defects seen in persons with hemifacial microsomia. The term oculo represents the eye, and the term auriculo represents the ear. Finally, the term vertebral stands for the physical problems present in the vertebrae.
Hemifacial microsomia is caused by a disruption of normal facial development. A baby's face forms very early, normally between the eighth and twelfth weeks of pregnancy. Normal facial development depends on many different tissues growing together. When the movement and development of these tissues is disrupted, the face may have abnormal openings, underdevelopment, and/or excess skin. In hemifacial microsomia, some unknown event disrupts normal development of the first and second branchial arches, the embryonic structures that later develop into the sides of face, the jaw, and the neck.
The possible causes for the embryonic disruption that leads to hemifacial microsomia are unknown. There are most likely many different factors that may lead to the abnormal development of the facial tissues. In some cases, these factors may be environmental. For example, there are certain medications a woman can take while pregnant that can cause the baby to have the symptoms of hemifacial microsomia. However, in the vast majority of cases, hemifacial microsomia is not caused by something taken during pregnancy.
In other cases, normal development of the facial tissues may be disrupted by genetic factors. The exact genetic factors are unknown. Unlike some other syndromes, there has not been a gene identified that, if changed, causes hemifacial microsomia. Studies in a few persons with hemifacial microsomia point to a possible causative genetic difference located on the long arm of chromosome 14; however, as of early 2005, this finding requires further study and characterization.
A few families in which hemifacial microsomia occurs show an autosomal recessive inheritance pattern, while other families show autosomal dominant pattern of inheritance. However, most cases of hemifacial microsomia are not inherited, meaning that it does not normally run in families.
Hemifacial microsomia typically occurs randomly. Doctors are often unable to explain why it developed. Since it is sporadic in nature, if a child is diagnosed with hemifacial microsomia, the risk for the parents to have another child with hemifacial microsomia is low. In rare cases, one parent may have some of the physical symptoms of hemifacial microsomia. If this is the case, then the risk to have a child with the disorder may be higher.
Holly Ann Ishmael MS, CGC, Judy C. Hawkins MS, CGC, Thomson Gale, Gale, Detroit,