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An infant with a small, posteriorly positioned mandible. The clinical urgency is airway: the tongue follows the small jaw posteriorly (glossoptosis) and can obstruct the oropharynx, especially supine. Micrognathia can be isolated, part of a sequence (a cascade from one defect), or a feature of a larger syndrome. The bedside task is to look in the mouth, listen to the breathing, and decide which work-up the constellation points toward.
Three branches to distinguish at the bedside:
- Isolated micrognathia: small jaw without other anomalies. Often catches up with growth; airway management may still be needed early.
- Pierre Robin sequence (PRS): micrognathia + glossoptosis + cleft palate (U-shaped, posterior). This is a sequence, not a syndrome: the small jaw in utero displaces the tongue, which physically blocks palatal shelf fusion. PRS itself is the finding, not the diagnosis. The question is always "what caused the micrognathia?"
- Syndromic micrognathia: bilateral mandibular hypoplasia plus other organ involvement points to a defined syndrome.
About 50% of Pierre Robin sequence is syndromic; Stickler is the single most common underlying syndrome in PRS and demands ophthalmology follow-up because of retinal detachment risk.
Pierre Robin sequence: what's driving the small jaw?
- Stickler syndrome (COL2A1, COL11A1, COL11A2, AD): the most common syndromic cause of PRS. Look for high myopia + vitreoretinal degeneration + sensorineural hearing loss + early-onset arthritis in the child or parents. The ophthalmology hook is the urgency: vitreoretinopathy means lifelong retinal detachment risk.
- 22q11.2 deletion syndrome: cleft palate (or VPI) + conotruncal cardiac + hypocalcemia + thymic hypoplasia + immune defect. Micrognathia is one feature among many; CMA or 22q FISH.
- Treacher Collins syndrome (TCOF1, POLR1C, POLR1D, AD): bilateral mandibular hypoplasia + downslanting palpebral fissures + coloboma of the lower eyelid + microtia/atresia + conductive hearing loss. The face is symmetric; cognition is normal. TCOF1 accounts for ~80%.
- Nager syndrome (SF3B4, AD; acrofacial dysostosis): Treacher-Collins-like face plus preaxial upper limb defects (radial hypoplasia, absent thumbs). The limb finding distinguishes it. (No condition leaf to link.)
- Cornelia de Lange syndrome (NIPBL, dominant): micrognathia + arched synophrys + long philtrum + upper-limb reduction + IUGR + ID.
Other causes of small jaw
- Achondrogenesis and other lethal skeletal dysplasias: micrognathia is part of a generalized chondrodysplasia; lethal in the perinatal period.
- Hemifacial microsomia / Goldenhar (OAVS): unilateral mandibular hypoplasia plus ipsilateral microtia and epibulbar dermoid; asymmetric, distinguishing it from Treacher Collins.
- Trisomy 18: micrognathia + clenched fists + rocker-bottom feet + IUGR.
- PRS + high myopia (parent or child) + early arthritis → Stickler. The first ophthalmology referral is the highest-leverage action.
- Cleft palate + conotruncal cardiac defect + hypocalcemia → 22q11.2 deletion.
- Bilateral symmetric mandibular hypoplasia + lower-lid coloboma + microtia, normal cognition → Treacher Collins (TCOF1).
- Treacher Collins facies + absent thumbs → Nager syndrome (acrofacial dysostosis with radial-ray involvement).
- Unilateral small jaw + ipsilateral ear malformation + epibulbar dermoid → hemifacial microsomia / Goldenhar (sporadic).
- Clenched fists + overlapping fingers + small jaw + IUGR → trisomy 18.
Before any genetics, the airway dominates the first 24-48 hours:
- Prone or lateral positioning displaces the tongue forward.
- Nasopharyngeal airway is the standard first-line adjunct in moderate cases.
- Polysomnography quantifies obstruction.
- Tongue-lip adhesion, mandibular distraction osteogenesis, or tracheostomy are escalating surgical options.
Feeding is the parallel problem: many infants need an upright-prone bottle position or a Haberman feeder, and a subset require NG or gastrostomy feeds.
- Direct exam of the palate: with a tongue blade and good light, look specifically for the U-shaped posterior cleft of PRS; submucous cleft is common and missed.
- Polysomnography to characterize and grade obstruction.
- Echocardiogram (22q11.2, syndromes with cardiac association).
- Renal ultrasound if 22q11.2 or syndromic picture.
- Hearing evaluation: conductive in Treacher Collins, sensorineural in Stickler.
- Ophthalmology consultation with dilated fundus exam: essential for Stickler (vitreoretinal disease + retinal detachment risk lifelong) and 22q11.2 (posterior embryotoxon).
- Chromosomal microarray + 22q11.2 FISH (CMA usually catches it).
- Targeted gene testing: Stickler gene panel (COL2A1/COL11A1/COL11A2), TCOF1/POLR1C/POLR1D if Treacher Collins suspected.
- Exome sequencing if syndromic pattern remains undefined.
- Pierre Robin is a sequence, not a syndrome. "Diagnose Pierre Robin" means "find the cause." Stickler is the leader; 22q11.2 and Treacher Collins are the other big two.
- Airway management precedes genetic testing. Position, NPA, and PSG come first.
- Stickler's retinal disease is lifelong. The ophthalmology referral done in the nursery is the action that prevents detachment-blindness decades later.
- Bilateral symmetric mandibular hypoplasia with lower-lid coloboma is the Treacher Collins exam in one line.
- Examine the parents. Stickler is autosomal dominant with variable expression; a mildly affected parent (myopia + early arthritis) may be the missing diagnostic piece.
- The cleft palate in PRS is U-shaped and posterior. Don't expect the typical V-shaped anterior cleft; submucous clefts are easy to miss without a careful exam.
- Tongue-lip adhesion is a temporizing measure, not a definitive correction. Mandibular distraction osteogenesis is increasingly preferred for moderate-to-severe airway compromise.
- Anticipate feeding difficulties. Many PRS infants need NG feeds or a Haberman bottle for the first months even after the airway stabilizes; nutrition support is part of the discharge plan.