Micrognathia (Small Lower Jaw) - Causes, Symptoms, Diagnosis, and Treatment

What Does Micrognathia Mean?

Micrognathia, otherwise called small jaw or mandibular hypoplasia, is when a child is born with or develops a smaller than normal lower jaw or mandible. The lower jaw of such a child is much shorter and smaller as compared to the rest of the face. It can be seen at birth or develop later in life. Micrognathia is associated with various syndromes, such as fetal alcohol syndrome, Pierre Robin syndrome, Treacher Collins syndrome, hemifacial microsomia, Stickler syndrome, etc., and genetic conditions like progeria and trisomy 13 and 18. Sometimes, the jaw grows with age, and the problem goes away, but in severe cases, micrognathia can lead to feeding problems, breathing difficulties, and malocclusion (misaligned teeth), as there is not enough space for all the teeth to grow in the small jaw.

Infants with micrognathia may need special nipples and have to be appropriately positioned to feed properly and to prevent cyanosis due to breathing problems. Prognosis depends on how small the jaw is, but outcomes are generally good.

What Are the Causes of Micrognathia?

People with a small jaw are usually born that way. In a few cases, genetic disorders are the cause, and in some, spontaneous genetic mutations are to blame. The following hereditary syndromes have micrognathia as a symptom:

• Pierre Robin Syndrome (or Sequence) - In this syndrome, the fetus’s jaw is formed slowly in the uterus, resulting in a comparatively smaller lower jaw. Smaller mandible makes the baby’s tongue fall back into the throat, which can choke the baby and make breathing difficult. Such babies also present with a cleft palate (a split in the roof of the mouth).

• Progeria - This genetic disorder makes the affected child age rapidly. The signs of progeria are not obvious at birth, but signs become more apparent in the first couple of years of life. Such children have a small lower jaw, hair loss, and narrow face.

• Trisomy 13 - Children born with trisomy 13, otherwise called Patau syndrome, is a chromosomal disorder, where instead of two copies, there are three copies of chromosome 13. Around 1 in 16,000 children are born with trisomy 13. Children born with trisomy 13 have low birth weight, cleft lip or palate, small lower jaw, and a small head.

• Trisomy 18 - Babies born with trisomy 18, otherwise called Edwards syndrome, have an extra chromosome 18 (three copies instead of two). About 1 in 6,000 children are born with this chromosomal abnormality, and it is the second most common trisomy syndrome after Down syndrome. Such babies might exhibit cleft palate, micrognathia, heart defects, small head, and deformed feet.

• Fetal Alcohol Syndrome - The maternal use of alcohol during pregnancy results in birth defects, such as craniofacial malformation and brain abnormalities. The facial deformities include short eyelid folds, upturned nose, thin upper lip, broad nasal bridge, and small lower jaw.

• Hemifacial Microsomia - Otherwise called Goldenhar syndrome, is a condition where one side of the face does not grow normally and is underdeveloped.

• Achondrogenesis - It is a rare genetic disorder where the pituitary gland does not make enough growth hormone, which leads to bone problems like a small mandible and narrow chest. Such babies have short legs, neck, arms, and torso.

• Cri-du-Chat Syndrome - Otherwise called 5p-syndrome or cat cry syndrome, is also a rare hereditary condition that causes physical deformities and developmental disabilities due to a missing genetic material on chromosome 5.

• Treacher Collins Syndrome (TCS) - A hereditary condition that causes serious facial abnormalities, such as a small jaw, cleft palate, ear malformation, and no cheekbones.

• Catel-Manzke Syndrome - A rare hereditary disorder that results in abnormalities of the index fingers and characteristics of Pierre Robin syndrome, such as micrognathia and cleft palate.

The other syndromes that can result in micrognathia are Marfan syndrome, Möbius syndrome, Prader-Willi syndrome, Silver-Russell syndrome, Wolf-Hirschhorn syndrome, Turner syndrome, etc.

What Are the Symptoms Associated With Micrognathia?

Children with micrognathia often show the following signs and symptoms:

• Failure to thrive - inadequate growth during early childhood.

• Infant apnea - temporary cessation of breathing.

• Feeding difficulties - the inability to feed, problems with latching, and insufficient weight gain.

• Noisy breathing.

• Tongue-tie - the tongue is attached to the mandible near the chin.

• Sleep disturbances.

• Glossoptosis - retraction or downward positioned tongue.

• Breathing problems - can result in cyanosis, where the baby’s skin or mucous membrane turns blue due to lack of oxygen.

When to Consult a Doctor for Micrognathia?

If your newborn’s jaw looks extremely small or if he or she is having trouble feeding, consult a doctor immediately. As some syndromes and genetic conditions associated with micrognathia are serious, prompt diagnosis and treatment are essential. Sometimes, your doctor might diagnose micrognathia before birth with an ultrasound.

How Does a Doctor Diagnose Micrognathia?

A small lower jaw can be clearly seen when its length is compared to the upper jaw. Once the doctor sees a discrepancy in the mandible size, he or she will conduct a physical examination to look for cleft palate, facial asymmetries, and tongue tie. If needed, the doctor will then order X-rays or a CT scan to define the anatomy of the face and head. A polysomnogram or sleep study might be needed to measure the child’s breathing, oxygenation during sleep, and brain and heart function.

How Is Micrognathia Treated?

The treatment options for micrognathia include:

1) Non-surgical Treatment -

• Make the child sleep in the prone position, on the stomach or chest, as it thrusts the base of the tongue forward and keeps the airway open.

• The airway can be kept open with the help of a flexible tube that is inserted into the child’s nasal passage through the nostril.

• Pressure ventilators like CPAP (continuous positive airway pressure) or BiPAP (Bi-level positive airway pressure) can be used for sleep apnea.

• Orthodontic treatment to correct a malocclusion.

2) Surgical Treatment -

• The tongue-tie is removed to allow easy moving of the tongue-base forward to keep the airway open.

• The mandible can be slowly lengthened to relieve the airway with mandibular distraction osteogenesis (MDO).

• Sometimes, an airway opening must be created in the neck (tracheostomy) to bypass the obstruction caused by a small jaw.

The prognosis for children with micrognathia is generally good, but it can vary based on the severity. Quick diagnosis and treatment, including surgeries, are essential to give the child the best long-term quality of life. The treatment plan will depend on the child’s jaw growth and development. For more information, consult a doctor online now.