(A) First (pharyngeal arch) (correct)

Pierre Robin sequence can be remembered as the mnemonic PRS:

• P - Palate cleft
• R - Respiratory obstruction (cyanotic spells)
• R - Retracted tongue
• S - Small mandible (micrognathia)

The sequence follows first from a hypoplastic and small mandible, which results in glossoptosis. The tongue then obstructs palatal fusion and a U-shaped palate. The tongue is then large relative to the jaw, resulting in airway obstruction.

PRS is an example of a first arch syndrome, the other being Treacher-Collins syndrome.

How to remember the first pharyngeal arch derivatives: All M s

• Maxillary process including the Maxilla and the zygoMatic bone
• Mandibular process including Meckel cartilage and the Mandible
• the Malleus and the incus, and the sphenoMandibular ligament
• the Muscles of Mastication