T-cell deficiencies Notes

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DiGeorge syndrome

NOTES NOTES T–CELL DEFICIENCIES GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Impaired function of T lymphocytes due to thymic hypoplasia → deficiency of cell-mediated immunity → high risk of infections ▪ Two main causes of thymic hypoplasia ▫ DiGeorge syndrome (DGS)/22q11.2 deletion syndrome ▫ Ataxia-telangiectasia (AT) syndrome (see Chapter 84 in Volume 1) ▪ Inherited, due to genetic defects ▪ Associated with other congenital abnormalities SIGNS & SYMPTOMS ▪ Recurrent infections; usually viral ▪ Depend on cause of thymic hypoplasia DIAGNOSIS LAB RESULTS Blood tests ▪ T cell numbers, function ▪ Calcium levels ▫ Hypocalcemia → DGS, eucalcemia → AT OTHER DIAGNOSTICS ▪ Genetic testing ▫ Identify genetic defect TREATMENT MEDICATIONS ▪ Management of symptoms ▫ Antibiotic therapy/prophylaxis for infections SURGERY ▪ Thymus transplantation OSMOSIS.ORG 217
DIGEORGE SYNDROME (DGS) osms.it/digeorge-syndrome PATHOLOGY & CAUSES ▪ AKA 22q11.2 deletion syndrome ▪ Genetic condition; q11.2 portion of DNA on chromosome 22 deleted → deletion of TBX gene on chromosome 22 → impaired development of pharyngeal pouches 3, 4 → hypoplasia of thymus, inferior parathyroid gland ▫ Deficiency in mature T cells, adaptive immune response: complete thymic aplasia can be fatal in first year of life ▫ Parathyroid hypoplasia → low levels of parathyroid hormone → hypocalcemia ▪ 22q11.2 region encodes genes that affect other organs/tissues → congenital cardiac defects; facial, developmental abnormalities; behavioral, mental health conditions SIGNS & SYMPTOMS ▪ Characteristic facial appearance: long face, small teeth, broad nose ▪ Developmental abnormalities (e.g. cleft palate) ▪ Cardiac defects (e.g. truncus arteriosus, tetralogy of Fallot) ▪ Thymus gland abnormalities → underdevelopment of cellular immune system → susceptibility to recurrent sinopulmonary infections/severe combined immunodeficiency (SCID) ▪ Learning difficulties/mental health conditions (e.g. schizophrenia) ▪ Hypoparathyroidism → hypocalcemia → seizures, tetany, osteoporosis DIAGNOSIS LAB RESULTS Blood tests ▪ Reduced T cell number, function ▪ Hypocalcemia ▪ Low levels of parathyroid hormone OTHER DIAGNOSTICS ▪ Genetic testing TREATMENT MEDICATIONS ▪ Management of symptoms ▫ Antibiotics for infections SURGERY ▪ Thymus transplantation OTHER INTERVENTIONS ▪ Vitamin D, calcium supplements for hypocalcemia Figure 35.1 A child with DiGeorge syndrome. 218 OSMOSIS.ORG

Osmosis High-Yield Notes

This Osmosis High-Yield Note provides an overview of T-cell deficiencies essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about T-cell deficiencies by visiting the associated Learn Page.