Mechanical basis The physical craniofacial deformities of<unk>  may be the result of a mechanical problem in which intrauterine growth of certain facial structures is restricted, or mandibular positioning is altered. One theory for the etiology of<unk>  is that, early in the first trimester of gestation, some mechanical factor causes the neck to be abnormally flexed such that the tip of the mandible becomes compressed against the sternoclavicular joint. This compression of the chin interferes with development of the body of the mandible, resulting in micrognathia. The concave space formed by the body of the hypoplastic mandible is too small to accommodate the tongue, which continues to grow unimpeded. With nowhere else to go, the base of the tongue is downwardly displaced, which causes the tip of the tongue to be interposed between the left and right palatal shelves. This in turn may result in failure of the left and right palatal shelves to fuse in the midline to form the hard palate. This condition manifests as a cleft palate. Later in gestation (at around 12 to 14 weeks), extension of the neck of the fetus releases the pressure on the mandible, allowing it to grow normally from this point forward. At birth, however, the mandible is still much smaller (hypoplastic) than it would have been with normal development. After the child is born, the mandible continues to grow until the child reaches maturity. Genetic basis Alternatively,<unk>  may also be caused by a genetic disorder. In the case of<unk>  which is due to a genetic disorder, a hereditary basis has been postulated, but it usually occurs due to a de-novo mutation. Specifically, mutations at chromosome 2 (possibly at the GAD1 gene), chromosome 4, chromosome 11 (possibly at the PVRL1 gene), or chromosome 17 (possibly at the SOX9 gene or the KCNJ2 gene) have all been implicated in<unk> . Some evidence suggests that genetic dysregulation of the SOX9 gene (which encodes the SOX-9 transcription factor) and/or the KCNJ2 gene (which encodes the Kir2.1 inward-rectifier potassium channel) impairs the development of certain facial structures, which can lead to<unk> .<unk>  may occur in isolation, but it is often part of an underlying disorder or syndrome. Disorders associated with<unk>  include Stickler syndrome, DiGeorge syndrome, fetal alcohol syndrome, Treacher Collins syndrome, and Patau syndrome.
Pierre Robin sequence
First arch syndrome
Roberts syndrome
XK aprosencephaly
Cleidocranial dysostosis
Spina bifida
Marden–Walker syndrome
Trismus pseudocamptodactyly syndrome