A sex chromosome in certain animals, such as chickens, turkeys, and moths. In humans, males are XY and females XX, but in animals with a Z chromosome, males are ZZ and females are WZ.

Zeta-chain-associated protein kinase 70. A member of the protein tyrosine kinase family, ZAP-70 is normally expressed in T cells and natural killer cells and has a critical role in the initiation of T-cell signaling. ZAP-70 is expressed in T cells and tumors of T-cell lineage. A high level of ZAP-70 expression appears restricted to T-cell […]

‘When you hear hoof beats, think of horses, not zebras.’ For example, when someone develops a mild transient cough, a virus infection is the most logical and likely cause, and tuberculosis is a zebra.

A gene that is lethal (fatal) for the zygote, the cell formed by the union of a sperm (male sex cell) and an ovum (female sex cell). The zygote would normally develop into an embryo, as instructed by the genetic material within the unified cell. However, a zygotic lethal gene scotches prenatal development at its […]

A technique in which a woman’s egg is fertilized outside the body, then implanted in one of her fallopian tubes. This technique is one of the methods used to overcome infertility, the inability of couples to produce offspring on their own. First, the egg and the male sperm needed to fertilize it are harvested. Then […]

Acanthosis nigricans: A skin condition characterized by dark, thickened, velvety patches, especially in the folds of skin in the armpit, groin, and back of the neck. It can occur with endocrine diseases such as Cushing disease and diabetes mellitus, from tumors of the pituitary gland, underlying malignancies, certain drugs, and as a genetic disorder. It […]

Celsus: (1st century A.D.) Aulus (Aurelius) Cornelius Celsus. Roman encyclopedist whose only surviving work, De Medicina, was rediscovered and printed early in the Renaissance and became influential. His four classical signs of inflammation — calor, dolor, rubor, and tumor (heat, pain, redness, and swelling) — are still useful today.

Fear of heat: Thermophobia. An abnormally excessive and persistent fear of heat, including hot weather and hot objects. Sufferers from this fear experience anxiety even though they realize their fear is irrational. To avoid heat, they may live in a cold climate, wear light clothing, stay indoors on warm days, and avoid hot water and […]

Blepharospasm: The involuntary, forcible closure of the eyelids. The first symptoms may be uncontrollable blinking. Only one eye may be affected initially, but eventually both eyes are usually involved. The spasms may leave the eyelids completely closed, causing functional blindness even though the eyes and vision are normal. Blepharospasm is a form of focal dystonia.

Disease, Kostmann: A condition with a lack of neutrophils (a type of white blood cell that is important in fighting infection). Children with this disease suffer frequent infections from bacteria which in the past led to death in three-quarters of cases before 3 years of age. This disease is also known as severe congenital neutropenia […]