[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [Head and neck: pharyngeal arches](https://durgical.com/en/embryology/#a-head_neck) › First-arch syndromes: Treacher Collins and Pierre Robin sequence [Embryology](https://durgical.com/en/embryology/) · [Head and neck: pharyngeal arches](https://durgical.com/en/embryology/#a-head_neck) # First-arch syndromes: Treacher Collins and Pierre Robin sequence - Malformation Defects of the jaw, cheekbones and ears because the first arch did not grow properly. They can make it hard for a newborn to breathe. Updated 2026-11-01 **See it in 3D:** [Mandible](https://durgical.com/en/anatomy/mandible/) · [Maxillae](https://durgical.com/en/anatomy/maxilla/) · [Zygomatic bones](https://durgical.com/en/anatomy/zygomatic-bone/) · [Malleus](https://durgical.com/en/anatomy/malleus/) · [Incus](https://durgical.com/en/anatomy/incus/) · [Auricle](https://durgical.com/en/anatomy/auricle/) · [Ear canal](https://durgical.com/en/anatomy/external-acoustic-meatus/) · [Tongue](https://durgical.com/en/anatomy/tongue/) · [Soft palate](https://durgical.com/en/anatomy/soft-palate/) ## Key points - Both are defects of the 1st arch and its neural crest. - Treacher Collins: TCOF1, autosomal dominant; hypoplastic zygoma and mandible, coloboma, conductive hearing loss. - Pierre Robin: micrognathia → glossoptosis → airway obstruction ± cleft palate. - Pierre Robin is a sequence, not a syndrome. - Look for Stickler or 22q11.2 in Pierre Robin. ## What it is First-arch syndromes are defects of the structures the first pharyngeal arch builds: mandible, maxilla, zygoma, ossicles and outer ear. The two most tested are Treacher Collins syndrome, a genetic mandibulofacial dysostosis, and the Pierre Robin sequence, in which a small mandible sets off the other findings. In both, the root problem is the neural crest that fills the first arch. ## Key facts - Treacher Collins: about 1 in 50,000 people (MedlinePlus). - Isolated Pierre Robin: between 1 in 8,500 and 1 in 14,000 (MedlinePlus). - 'Sequence' means one first defect (the mandible) produces the others in a chain. ## Embryological cause - Treacher Collins: variants in TCOF1 (most cases; treacle protein), POLR1D (both autosomal dominant, about 60% new) or POLR1C (recessive). - These genes help make ribosomal RNA; their failure causes excess death of 1st- and 2nd-arch neural crest cells, although migration is normal. - Pierre Robin: the first defect is a small mandible (micrognathia), which leaves the tongue back (glossoptosis), between the palatal shelves, and blocks palate closure (weeks 7–10). - Pierre Robin can be isolated (changes near SOX9), part of a syndrome (Stickler, 22q11.2) or a deformation from chin compression (oligohydramnios). - Teratogens such as isotretinoin and alcohol can injure first-arch neural crest and give similar pictures. ## How it presents - Treacher Collins: underdeveloped cheekbones and mandible, down-slanting palpebral fissures, lower eyelid coloboma and sparse lashes. - Treacher Collins: small or absent ears, ear canal atresia and conductive hearing loss in about half; intelligence usually normal. - Pierre Robin: triad of micrognathia, glossoptosis and airway obstruction; most have a U-shaped cleft palate. - Both can cause breathing and feeding problems from birth. - Differential: hemifacial microsomia (oculo-auriculo-vertebral spectrum), usually asymmetric. ## Diagnosis - Prenatal ultrasound: small, receding mandible on the fetal profile, sometimes with polyhydramnios from poor swallowing. - At birth: airway and feeding assessment; sleep study if there is obstruction. - Early hearing assessment, especially in Treacher Collins. - Genetic testing (TCOF1, POLR1C, POLR1D; look for Stickler or 22q11.2 in Pierre Robin). ## Memory aid In Pierre Robin everything falls like dominoes from the jaw: small chin, tongue back, palate open, airway narrow. ## Test yourself Think of the answer, then tap the question to see it. ## What is the first defect in the Pierre Robin sequence? The small mandible (micrognathia), which pushes the tongue back and blocks palate closure. ## Which gene is most often altered in Treacher Collins syndrome? TCOF1, which encodes the treacle protein; inheritance is autosomal dominant. ## Why is there conductive hearing loss in Treacher Collins syndrome? Because 1st- and 2nd-arch derivatives are affected: ossicles, external ear canal and auricle. ## Which embryonic cells fail in both conditions? The neural crest cells that form the mesenchyme of the first arch. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/embryology/first-arch-syndromes-treacher-collins-and-pierre-robin-sequence/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Mandible](https://durgical.com/en/anatomy/mandible/) - [Maxillae](https://durgical.com/en/anatomy/maxilla/) - [Zygomatic bones](https://durgical.com/en/anatomy/zygomatic-bone/) - [Malleus](https://durgical.com/en/anatomy/malleus/) - [Incus](https://durgical.com/en/anatomy/incus/) - [Auricle](https://durgical.com/en/anatomy/auricle/) - [Ear canal](https://durgical.com/en/anatomy/external-acoustic-meatus/) - [Tongue](https://durgical.com/en/anatomy/tongue/) - [Soft palate](https://durgical.com/en/anatomy/soft-palate/) ## Related - [First pharyngeal arch (mandibular arch) and the trigeminal nerve](https://durgical.com/en/embryology/first-pharyngeal-arch-and-the-trigeminal-nerve/) - [Neural crest cells and their derivatives](https://durgical.com/en/embryology/neural-crest-cells-and-their-derivatives/) - [The face: five prominences](https://durgical.com/en/embryology/the-face-five-prominences/) - [Palate: primary and secondary palate](https://durgical.com/en/embryology/palate-primary-and-secondary-palate/) - [Cleft lip and cleft palate](https://durgical.com/en/embryology/cleft-lip-and-cleft-palate/) - [Congenital hearing loss, microtia and preauricular pits](https://durgical.com/en/embryology/congenital-hearing-loss-microtia-and-preauricular-pits/) - [Ear: inner, middle and external ear](https://durgical.com/en/embryology/ear-inner-middle-and-external-ear/) - [Isotretinoin and other retinoids](https://durgical.com/en/embryology/isotretinoin-and-other-retinoids/) - [Tongue: development and innervation](https://durgical.com/en/embryology/tongue-development-and-innervation/) ## Related conditions - [Cleft lip and palate](https://durgical.com/en/conditions/cleft-lip-and-palate/) - [Hearing loss (conductive and sensorineural, including sudden hearing loss)](https://durgical.com/en/conditions/hearing-loss/) - [Obstructive sleep apnoea](https://durgical.com/en/conditions/obstructive-sleep-apnoea/) [← All of embryology](https://durgical.com/en/embryology/) Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given. Sources: [Treacher Collins syndrome: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/treacher-collins-syndrome/) (National Library of Medicine (MedlinePlus), 2022); [Isolated Pierre Robin sequence: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/isolated-pierre-robin-sequence/) (National Library of Medicine (MedlinePlus), 2016); [Embryology, Branchial Arches - StatPearls - NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK538487/) (StatPearls Publishing (NCBI Bookshelf), 2023); Langman's Medical Embryology, 13th ed., ch. 17: Head and Neck (Wolters Kluwer, 2015). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/embryology/first-arch-syndromes-treacher-collins-and-pierre-robin-sequence/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/first-arch-syndromes-treacher-collins-and-pierre-robin-sequence/