Definition is a rhetorical mode that can be used in something smaller or shorter than a full paper. You can use extended definition for several paragraphs only in a paper of much greater length. You also can add to a paper a one-paragraph definition--like a brief encyclopedia definition.
Immunodeficiency: Therapies include thymus transplantation and adoptive transfer of mature T cells (ATMTC) for individuals with complete DiGeorge syndrome and appropriate prophylaxis measures and monitoring autoimmune complications for incomplete or partial DiGeorge syndrome.
Low parathyroid hormone levels can cause the blood calcium to be low. A number of conditions, such as DiGeorge syndrome, may cause low parathyroid hormone levels. Hypocalcemia is more common in premature and low birthweight babies.