thymic hypoplasia

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A developmental failure of the thymus and parathyroid leading to an absence of T cells and defective cell-mediated immunity. It is due to a hemizygous deletion of 1.5–3.0 Mbp from chromosome 22q11.2 leading to haploinsufficiency of the TBX1 (T-box 1) transcription factor gene, or point mutations in the TBX1 gene. Hypoplasia of the parathyroid causes hypocalcaemia and there are other developmental abnormalities associated with the syndrome and caused by defects in cervical neural crest migration.

Subjects: Medicine and Health.

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