This is because the 22q11 region has a structure that makes it highly prone to rearrangements during sperm or egg formation.The exact mechanism that causes all of the associated features of the syndrome is unknown. Of the 30–50 genes in the deleted region, a number have been identified as possibly playing a role in the development of some of the signs and symptoms. TBX1
Haploinsufficiency of the TBX1 gene (T-box transcription factor TBX1) is thought to be the cause of some of the symptoms observed. Point mutations in this gene have also been observed in individuals with DiGeorge syndrome. TBX1 is part of the T-box family of genes which have an important role in tissue and organ formation during embryonic development and it may have a role in the regulation of differentiation of post migration neural crest cells. The neural crest forms many of the structures affected in DiGeorge syndrome, including  the skull bones, mesenchyme of the face and palate, the outflow tract of the heart, and the thymus and parathyroid stroma. When there is a loss of expression of FGF18 during the development of the pharyngeal arches, neural crest cell death is seen. Although neither FGF18 or TBX1 are expressed in the neural crest cells, TBX1 might have a role in the regulation of FGF18 expression, ensuring that the differentiation of these cells in the pharyngeal region is correct.
Prognosis
The prognosis of ectopia cordis depends on classification according to three factors:
Location of the defect
Cervical
Thoracic
Thoracoabdominal
Abdominal
Extent of the cardiac displacement
Presence or absence of intracardiac defectsSome studies have suggested a better prognosis with surgery in cases of thoracoabdominal ectopia cordis or less severe pentalogy of Cantrell. In general, the prognosis for ectopia cordis is poor—most cases result in death shortly after birth due to infection, hypoxemia, or cardiac failure. Epidemiology
The occurrence of ectopia cordis is 8 per million births. It is typically classified according to location of the ectopic heart, which includes:

Cervical
Thoracic
Thoracoabdominal
AbdominalThoracic and thoraco-abdominal ectopia cordis constitute the vast majority of known cases. References


== External links ==