Micrognathia · What Is It, Diagnosis, Treatment, and More

Micrognathia can be caused by genetic factors and is often seen as a part of certain inherited syndromes, including Pierre Robin sequence, Treacher-Collins syndrome, Marfan syndrome, and Turner syndrome. Pierre Robin sequence is a common birth defect characterized by micrognathia, as well as glossoptosis (i.e., downward displacement or retraction of the tongue) and airway obstruction. It can be caused by a genetic mutation or overcrowding in the uterus, as is seen with twin pregnancies. Treacher-Collins syndrome is a genetic disorder that affects the growth and development of the head and tissues of the face. Marfan syndrome is an inherited disorder primarily affecting the body’s connective tissue. Finally, Turner syndrome is caused by the partial or complete absence of one X chromosome in those assigned female at birth. 

In addition to genetic factors, environmental factors including exposure to toxins or medications during pregnancy can influence the development of the jaw. Ingestion of alcohol by a pregnant individual can lead to fetal alcohol syndrome (FAS). Children with FAS may have distinctive facial features, including micrognathia, in addition to a wide range of developmental and neurological problems.  

Other risk factors include tobacco use and the use of certain prescription medications, including antiepileptics (e.g., phenytoin) and retinoids (e.g., isotretinoin for acne treatment) during pregnancy. Environmental pollutants such as heavy metals (e.g., lead, mercury) and chemicals (e.g., pesticides) can also disrupt fetal development and contribute to micrognathia. Lastly, certain risk factors, including a family history of facial anomalies and genetic syndromes, can increase the likelihood of micrognathia. 

The sign of micrognathia includes a smaller, retruded jaw. Associated symptoms can differ depending on the individual's age and the severity of the micrognathia. In neonates and infants, micrognathia is more likely to cause upper airway obstruction resulting in difficulty breathing. In some cases, the jaw may be small enough to interfere with proper feeding in infants, and in older children micrognathia is often primarily a cosmetic concern, causing facial asymmetry. Additionally, micrognathia may cause dental problems such as misalignment and overcrowding of the teeth. Jaw misalignment may also lead to speech problems including difficulty articulating sounds. In both children and adults, the posterior positioning of the jaw can make intubation difficult during anesthesia or in emergencies. Of note, in some cases micrognathia can correct itself during puberty. 

In the case that micrognathia is associated with the Pierre Robin sequence, the individual may also have a cleft palate, or an opening in the roof of the mouth; gastroesophageal reflux; and conductive hearing loss. Those with micrognathia secondary to Treacher-Collins also have underdeveloped facial bones, particularly of the cheekbones. Those with Marfan syndrome often have a tall stature and long limbs. Lastly, those with Turner syndrome often have a neck webbing and a low hairline at the back of the neck in addition to micrognathia.  

The diagnosis of micrognathia is often made based on a review of symptoms, medical history, and physical examination. The healthcare professional may ask about a family history of genetic disorders and perform a comprehensive examination of the facial structure to assess the child’s jaw size and relation to other facial features. While imaging is not typically necessary to diagnose micrognathia, X-ray imaging, ultrasound, and magnetic resonance imaging (MRI) may provide detailed views of the bone structure to assess the severity and help plan for treatment. In some cases, a sleep study may be performed to assess for sleep apnea, considering that the position of the jaw and tongue may lead to an increased risk of airway obstruction and obstructive sleep apnea (ie., a condition in which breathing starts and stops during sleep due to collapse of the airway).  

In cases where a syndrome is suspected, genetic tests may be conducted to identify specific abnormalities that could explain the micrognathia. A prenatal ultrasound or MRI can also be done to assess for the presence of micrognathia or a cleft palate.  

Treatment for micrognathia depends on the severity of the condition. In mild cases, immediate treatment is often not necessary. Additionally, children with micrognathia may outgrow the condition as they age and their jaw increases in size, which is another benefit of delaying treatment until the child is older. In these instances, close monitoring can ensure that breathing, feeding, and speech development are occurring as expected. Dental braces or other orthodontic treatments can help align the teeth and improve jaw function, when needed.  

In more severe cases, if the infant has trouble feeding due to micrognathia, they may require the use of specialized nipples for bottle feeding, or the use of a tube inserted through the nose into the stomach for nutritional support.  

Surgical options may also be considered in severe cases where feeding and breathing are affected, or they may be considered later in adolescence once the bones have matured. The goal of surgery is to extend and lengthen the lower jawbone, and this may be done through mandibular distraction osteogenesis (MDO). In MDO, the surgeon typically makes cuts on both sides of the lower jaw and attaches special equipment that helps to move the bottom jaw forward.   

Regardless of severity, treatment often involves an interdisciplinary care team of pediatric otolaryngologists, craniofacial specialists, geneticists, pediatric pulmonologists, and speech therapists to provide individualized, comprehensive care.  

For cases linked to genetic conditions, genetic counseling may be offered to the individual and their family.