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Determining the severity of immunodeficiency in infants with 22q11.2 deletion/DiGeorge syndrome

Determining the severity of immunodeficiency in infants with 22q11.2 deletion/DiGeorge syndrome
DGS is a constellation of signs and symptoms associated with defective development of the pharyngeal pouch system. The classic triad of features on presentation is conotruncal cardiac anomalies (truncus arteriosus, tetralogy of Fallot, interrupted aortic arch or aberrant right subclavian), hypoplastic thymus, and persistent hypocalcemia resulting from parathyroid hypoplasia. Most patients with DGS have 22q11.2 deletion syndrome (22qDS or 22q11del). This deletion causes DGS and other similar syndromes. It is important to determine the type and degree of immunodeficiency in infants with 22qDS/DGS because it impacts management. Severe T cell immunodeficiency due to congenital athymia (complete DGS) is rare. Some of these infants also have autologous immune dysregulation with skin and gastrointestinal manifestations and a poorly functioning oligoclonal T cell population (atypical complete DGS or Omenn-like syndrome). Most patients have some degree of thymic insufficiency and T cell lymphopenia (partial DGS) and may also have humoral immunodeficiencies.

22qDS: 22q11.2 deletion syndrome; CDR: complementarity-determining region; DGS: DiGeorge syndrome; IgE: immunoglobulin E; IgM: immunoglobulin M; SCID: severe combined immunodeficiency; TREC: T cell receptor excision circle.

* Use of the term 22qDS is preferred for patients with this genetic defect and a DGS phenotype, with the term DGS reserved for patients who have phenotypic features consistent with DGS but do not have a 22q11.2 deletion (they may have a different pathogenic variant associated with the syndrome or no identified genetic defect).

¶ More extensive testing prior to definitive therapy is recommended because the rare presence of other inborn errors of immunity may impact choice of therapy (thymic transplant versus hematopoietic cell transplantation). Patients also rarely have coexisting conditions due to other genetic defects.

Δ Refer to UpToDate topics on 22q11.2 deletion/DiGeorge syndrome for details on diagnosis and differential diagnosis.

◊ B cell function can be assessed by measuring IgM levels. Refer to UpToDate topics on humoral immunodeficiency and laboratory evaluation of the immune system for additional details.
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