AIDS dementia complex A brain disorder in people with severe AIDS, causing loss of thinking capacity and affecting the ability to function. AIDS dementia complex is considered an AIDS-defining illness—that is, one of the serious illnesses that occurs in HIV-positive individuals warranting an AIDS diagnosis, according to the definition of AIDS by the Centers for…
AIDS Acquired immunodeficiency syndrome, a syndrome caused by infection with the human immunodeficiency virus (HIV), with ensuing compromise of the body’s immune system. Features include deficiency of certain types of leukocytes, especially T cells; infection with opportunistic infections that take advantage of the impaired immune response, such as tuberculosis, bacterial pneumonia, human herpes virus, or…
AID Artificial insemination by donor.
Aicardis syndrome A rare genetic disorder that occurs only in females and is caused by congenital absence of the corpus callosum, a large bundle of nerves that connects the left and right sides of the brain. Features include epilepsy that emerges in infancy and is difficult to control, vision problems due to maldeveloped retinas, developmental…
agreement, arbitration See arbitration agreement.
agranulocytosis, infantile genetic An inherited condition characterized by a lack of granulocytes (neutrophils), a type of white blood cell that is important in fighting infection, and a predisposition to frequent bacterial infections. Also known as Kostmann disease or syndrome and genetic infantile agranulocytosis. See also agranulocytosis; granulocytopenia; severe congenital neutropenia.
agranulocytosis A marked decrease in the number of granulocytes (neutrophils). Agranulocytosis results in frequent chronic bacterial infections of the skin, lungs, throat, and other areas. It can be an inherited genetic condition or acquired as, for example, in leukemia. See also agranulocytosis, infantile genetic; granulocytopenia; severe congenital neutropenia.
agoraphobia An abnormal and persistent fear of public places or open areas, especially those from which escape could be difficult or in which help might not be immediately accessible. Persons with agoraphobia frequently also have panic disorder. People with mild agoraphobia often live normal lives by avoiding anxiety-provoking situations. In the most severe agoraphobia, the…
agonist A substance that acts like another substance and therefore stimulates an action. Agonist is the opposite of antagonist. Antagonists and agonists are key players in the chemistry of the human body and in pharmacology.
agnosia An inability to recognize sensory inputs such as light, sound, and touch). Agnosia is typically a result of brain injury. For example, damaging the back part of the brain can cause visual agnosia (inability to properly recognize objects by sight).
aggressive fibromatosis See desmoid tumor.
aggressive 1 In cancer medicine, quickly growing or tending to spread rapidly. For example, an aggressive tumor. 2 In psychiatry, having a tendency to aggression or belligerent behavior.