Lesch-Nyhan syndrome A rare, inherited disorder caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). The lack of HPRT causes a buildup of uric acid in all body fluids, and leads to symptoms such as severe gout, poor muscle control, and moderate retardation, which appear in the first year of life. Affected individuals also…
lesion An area of abnormal tissue change. Lesions vary in severity from harmless to serious.
let-down reflex An involuntary reflex during breastfeeding that causes the milk to flow freely.
lethal Deadly.
lethargy Abnormal drowsiness, stupor.
Letterer-Siwe disease A form of Langerhans cell histiocytosis starting in infancy that involves proliferation of histiocytes in multiple organs such as the skin, bones, and other organs. Symptoms include rash, swollen glands, enlargement of the liver and spleen, liver disease, anemia, and lytic lesions of the bones. Letterer-Siwe disease is the most severe form of…
leukemia Cancer of the blood cells. Strictly speaking, leukemia should refer only to cancer of the white blood cells (leukocytes), but in practice it can apply to malignancy of any cellular element in the blood or bone marrow, as in red cell leukemia (erythroleukemia). Treatment may involve chemotherapy, radiation therapy, biological therapy, and/or bone marrow…
leukemia, acute lymphoblastic A form of leukemia that has a sudden onset and is characterized by the presence in the blood and bone marrow of large numbers of unusually immature white blood cells that are precursors of lymphocytes (lymphoblasts). Lymphoblasts are rarely seen in the blood under normal circumstances. Abbreviated ALL. Treatment for ALL may…
leukemia, acute myeloid A quickly progressive malignancy in which there are too many immature blood-forming cells that are precursors to the granulocytes or monocytes in the blood and bone marrow. Abbreviated AML. AML can occur in children and adults. In AML, the red blood cell levels may be low, causing anemia; platelet levels may be…
laughing gas See nitrous oxide.
lavage Washing out. Gastric lavage, for example, is the washing out of the stomach to remove drugs or poisons.
law, Hardy-Weinberg See Hardy-Weinberg law.