DiGeorge (22q11.2 deletion) syndrome: Epidemiology and pathogenesis
- Christine M Seroogy, MD
Christine M Seroogy, MD
- Associate Professor
- University of Wisconsin Medical School
DiGeorge syndrome (DGS) is a constellation of signs and symptoms associated with defective development of the pharyngeal pouch system. Most cases are caused by a heterozygous chromosomal deletion at 22q11.2. The classic triad of features of DGS on presentation is conotruncal cardiac anomalies, hypoplastic thymus, and hypocalcemia (resulting from parathyroid hypoplasia).
Thymic hypoplasia in DGS results in a range of T cell deficits. The majority of patients with DGS have mild defects in T cell numbers and are not clinically immunodeficient. Approximately 0.5 to 1 percent, however, have a complete absence of thymic tissue and profound immunodeficiency. This form of DGS, called complete DGS, is a type of severe combined immunodeficiency (SCID), and is life-threatening if not corrected with immune reconstitution.
This topic reviews the epidemiology and pathogenesis of DGS. The clinical features, diagnosis, management, and prognosis of patients with DGS are presented separately. (See "DiGeorge (22q11.2 deletion) syndrome: Clinical features and diagnosis" and "DiGeorge (22q11.2 deletion) syndrome: Management and prognosis".)
The clinical features of DiGeorge syndrome (DGS) were first described in 1829, and congenital absence of the thymus and parathyroid glands was reported by Dr. Angelo DiGeorge in 1965 . In the 1980s, it was discovered that deletions in chromosome 22q11.2 were present in most patients with DGS, as well as in patients with other similar syndromes, such as velocardiofacial syndrome (VCFS, also called Shprintzen syndrome) [2-4].
Thus, these conditions can be grouped together under the term chromosome 22q11.2 deletion syndrome (22qDS). Patients with the DiGeorge phenotype and the chromosome 22q11.2 deletion are most precisely referred to as having "DGS with chromosome 22q11.2 deletion" and those with other mutations are referred to as having "DGS without chromosome 22q11.2 deletion" . Other syndromes associated with deletions in chromosome 22q11.2 are mentioned briefly and reviewed in more detail elsewhere. (See "Syndromes with craniofacial abnormalities".)
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