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.
It is a disorder that is caused by a microdeletion in chromosome band 22q11.2. The key gene that is lost is Tbx-1, a control gene that regulates other genes required for the connection of the heart with the blood circulation. Tbx-1 also controls genes involved in the development of the parathyroid and thymus glands and the shape of the face. Babies with DiGeorge syndrome are born with hypocalcemia, congenital heart disease, cleft lip and/or palate, and are highly susceptible to infections.