Birth Defects Involving the Pharyngeal Apparatus

Practice flashcards covering the etiology and phenotypes of human congenital defects related to the pharyngeal apparatus development.

Syndrome

A group of abnormalities occurring together.

$22q11.2$ Deletion Syndrome

Also called DiGeorge syndrome or Velocardiofacial syndrome (VCFS), it is caused by a $1.5 - 3\,\text{Mb}$ heterozygous deletion on chromosome $22q11.2$, occurring in $1\,\text{in}\,\sim 3000$ live births.

$TBX1$ ($T\text{-box } 1$)

A key etiologic gene in $22q11.2$ Deletion Syndrome that encodes a transcription factor expressed in the ectoderm, endoderm, and mesoderm of the pharyngeal arches.

Micrognathia

A term describing a small lower jaw, seen as a craniofacial phenotype in syndromes like $22q11.2$ Deletion and Treacher Collins.

Hypocalcemia

Low serum calcium levels that might cause seizures, resulting from impaired or failed development of the parathyroid glands from the $3\text{rd}$ Pharyngeal Pouch.

Treacher Collins Syndrome

Also called Mandibulofacial Dysostosis, it is a disorder affecting craniofacial development ($1\text{st}$ pharyngeal arch) characterized by micrognathia, hypoplastic zygomatic arches, and lower eyelid coloboma, occurring in $1\,\text{in}\,\sim 10,000$ births.

$$TCOF1$$

The gene which, when mutated, causes Treacher Collins Syndrome; it encodes a protein called 'treacle' involved in ribosome ($rRNA$) production.

Treacle

A protein involved in making ribosomes that is encoded by the $TCOF1$ gene; its haplo-insufficiency leads to a deficiency in neural crest cells.

(Pierre) Robin Sequence

A developmental disorder (occurring $1\,\text{in}\,\sim 8500$ births) involving a chain of malformations: micrognathia, glossoptosis, and cleft secondary palate.

Glossoptosis

The downward displacement or retraction of the tongue, often seen in Pierre Robin Sequence.

Goldenhar Syndrome

Also known as Oculoauriculovertebral spectrum or Hemifacial microsomia, it involves the unilateral under-development of the oral-facial area, involving the $1\text{st}$ and $2\text{nd}$ pharyngeal arches.

Branchial Fistula (External)

A condition occurring when the $2\text{nd}$ pharyngeal arch fails to grow caudally over the $3\text{rd}$ and $4\text{th}$ arches, keeping the pharyngeal clefts in contact with the surface.

Lateral Cervical Cyst

A cyst resulting from the failure of the cervical sinus to disappear during development, often found anterior to the sternocleidomastoid muscle.

Thyroglossal Cyst

A cyst that forms if the thyroglossal duct fails to disappear during the migration of the thyroid gland from the foramen cecum; it is always located close to the midline.

Ankyloglossia

Commonly known as Tongue Tie, a condition where the tongue is not freed from the floor of the mouth due to the frenulum at the tip, affecting feeding and speech.