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A group of phenotypically variable, mostly sporadic conditions caused by 1.5- to 3.0-Mb hemizygous deletions of chromosome 22q11.2. Haploinsufficiency of the TBX1 gene encoding the transcription factor T-box 1 is believed responsible for most of the physical findings. Clinical features may include cardiac anomalies, including truncus arteriosus and tetralogy of Fallot, as well as other anomalies, including micrognathia, thymic aplasia (with resultant immunodeficiency), cleft palate, and hypoparathyroidism.
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