PARATHYROIDS, HYPOPLASIA OF THE THYMUSAND

Also known as the DiGeorge syndrome (DGS), this disorder is characterized by (1) low blood calcium levels (hypocalcemia) due to underdevelopment (hypoplasia) of the parathyroid glands which control calcium; (2) underdevelopment (hypoplasia) of the thymus, an organ behind the breastbone in which lymphocytes mature and multiply; and (3) defects of the heart involving the outflow tracts from the heart. Most cases of DGS are due to a microdeletion in chromosome band 22q11.2. A small number of cases have defects in other chromosomes, notably 10p13. Named after the American pediatric endocrinologist Angelo DiGeorge. Another name for DGS is the third and fourth pharyngeal pouch syndrome.