ABSTRACT
22q11.2 deletion syndrome is the commonest chromosome deletion syndrome.Most patients with DiGeorge anomaly have monosomic deletions of chromosome 22q11.2.Abnormal pharyngeal arch development results in defects in the development of the parathyroid glands,thymus and conotruncal region of the heart.Defective thymus development is associated with impaired immune function." Complete" DiGeorge syndrome accounts for ＜ 0.5％ of patients with total absence of the thymus and a severe T cell immunodeficiency.Most patients with partial defects have variable T cell deficiency.There is a wide phenotypic spectrum including speech delay,neuropsychiatric disorders and otolaryngological disorders.These patients are at increased risk of a variety of autoimmune diseases.Severe cases need thymus transplantation.