Micrognathia

Micrognathia can be due to a short mandible or a backward displacement of the mandible. It is seen in 1 in 1,500 live births.

Immediate morbidity and mortality depends on appropriate expertise at birth to facilitate airway management. Longer-term morbidity and mortality is largely determined by an underlying diagnosis and/or associated anomalies.

Polyhydramnios is an antenatal feature of severe micrognathia owing to obstruction of the gastrointestinal tract by the tongue.

There may be associated multi-systemic anomalies, such as skeletal, cardiovascular, neurological and craniofacial defects. The more anomalies present, the greater possibility of an underlying genetic diagnosis.

Watch this brief ultrasound video from the Fetal Medicine Foundation to see how features of micrognathia can be identified during the 20-week scan.

• Around 30% of micrognathia cases will have an underlying chromosomal anomaly, particularly trisomy 18 and triploidy.
• Micrognathia can be associated with various genetic syndromes, including the below.
  • Pierre Robin sequence is a combination of micrognathia, cleft palate and glossoptosis. Some cases are associated with an underlying genetic diagnosis and/or other structural anomalies.
  • Treacher Collins syndrome involves hypoplasia of the maxilla and zygoma, micrognathia, cleft palate and malformed or absent ears. Nearly all cases of Treacher Collins syndrome have heterozygous variants in TCOF1, POLR1D or POLR1B, or homozygous variants in POLR1C or POLR1D, while around 3% will not have an identified genetic cause.
  • Otocephaly (or Agnathia-Microstomia-Synotia syndrome) is associated with severe micrognathia or agnathia with midline anomalies including holoprosencephaly, encephalocele, cyclopia, aglossia or midline ear positioning. So far, variants in OTX2 and PRRX1 have been linked with this condition.

Micrognathia may be diagnosed prenatally on ultrasound scan, or postnatally on clinical and radiological features.

For information on genomic testing, see:

• Fetus with anomalies discovered during the mid-trimester anomaly scan;
• Infant with congenital malformation and dysmorphism syndrome; and
• Clinical suspicion of Edwards syndrome (trisomy 18).

Recurrence of this condition depends on the underlying cause. Isolated micrognathia has no increased risk of recurrence; however, where a common aneuploidy is diagnosed, the recurrence risk is around 1%. If a genetic syndrome or single-gene disorder is identified, the recurrence risk is 25%–50%, depending on the inheritance pattern.

The management of micrognathia depends on its severity, as well as on the presence of any associated anomalies.

Antenatal management

• Regular ultrasound monitoring is advised every four weeks during the antenatal period.
• If multiple associated anomalies are found, further investigations involving fetal medicine and clinical genetics teams may be considered.

Delivery

• Where significant micrognathia is expected, there can be difficulties with airway management at birth. Delivery should therefore be planned in a unit with appropriate expertise for difficult airway management in a neonate.
• Delivery should be timed to facilitate appropriate neonatal cover at the time of birth, in case of complications. This is usually at around 38 weeks.
• There is no contraindication to vaginal birth, though elective caesarean section is sometimes preferred for planning purposes.

Postnatal management

• Immediate availability of the airway management team is required.
• Multidisciplinary management, including specialist neonatal and paediatric care, is required.

For clinicians

• GeneReviews: Treacher Collins syndrome
• NHS England: National Genomic Test Directory
• StatPearls: Pierre Robin syndrome
• The Fetal Medicine Foundation: Micrognathia
• The Fetal Medicine Foundation: Micrognathia (video, 32 seconds)

References:

• Antonakopoulos N and Bhide A. ‘Focus on prenatal detection of micrognathia‘. Journal of Fetal Medicine 2019: volume 6, issue 3, pages 107–112. DOI: 10.1007/s40556-019-00210-0
• Jagtap SV, Saini N, Jagtap S and others. ‘Otocephaly: Agnathia-Microstomia-Synotia syndrome – A rare congenital anomaly‘. Journal of Clinical and Diagnostic Research 2015: volume 9, issue 9, pages ED03–ED04. DOI: 10.7860/JCDR/2015/13636.6444
• Paladini D. ‘Fetal micrognathia: Almost always an ominous finding‘. Ultrasound in Obstetrics & Gynaecology 2010: volume 35, issue 4, pages 377–384. DOI: 10.1002/uog.7639
• Sergouniotis PI, Urquhart JE, Williams SG and others. ‘Agnathia-otocephaly complex and asymmetric velopharyngeal insufficiency due to an in-frame duplication in OTX2‘. Journal of Human Genetics 2015: volume 60, issue 4, pages 199–202. DOI: 10.1038/jhg.2014.122

For patients

• Cleft Lip & Palate Association: Pierre Robin sequence
• International Society of Ultrasound in Obstetrics and Gynaecology: Micrognathia