Dictionary

XY The most frequent sex chromosome complement in human males. See also X chromosome; Y chromosome.

xylitol A sweetener that is found in plants and used as a substitute for sugar. Xylitol is called a nutritive sweetener because it provides calories, just like sugar. However, it is less likely than sugar to contribute to dental caries.

XYY syndrome A chromosomal disorder that affects about 1 in 1,000 males caused by the presence of an extra Y chromosome. Symptoms may include increased height, speech delays, learning disabilities, mild to moderate mental retardation, and behavioral disturbances. Also known as polysomy Y syndrome.

Y 1 In chemistry, the symbol for the element yttrium, an extremely rare metal that has been used in certain nuclear medicine scans. 2 In genetics, the Y chromosome.

WS Waardenburg syndrome.

Wt Abbreviation for weight. For example, “Wt 80 lbs” means “weight 80 pounds.”

X In genetics and medicine, X chromosome.

X chromosome The sex chromosome that is found twice in normal females and singly, along with a Y chromosome, in normal males. The complete chromosome complement consists of 46 chromosomes, including the 2 sex chromosomes, and is thus conventionally written as 46,XX for chromosomally normal females and 46,XY for chromosomally normal males.

xanthelasma Tiny, slightly raised, yellowish plaques on the skin surface of the upper or lower eyelids. Xanthelasma is a harmless growth of tissue caused by tiny deposits of fat in the skin, and it is often associated with abnormal blood fat levels (hyperlipidemia). Xanthelasma is composed of lipid-laden foam cells called histiocytes. Treatment is directed…

xanthinuria A rare metabolic disorder that is caused by lack of an enzyme needed to process xanthine, an alkaloid found in caffeine; theobromine; theophylline; and related substances. Unchecked, xanthinuria can lead to kidney stone formation. Treatment involves avoiding foods and drinks that contain xanthine derivatives, such as coffee, tea, and cola. Classic xanthinuria is inherited…

xanthoma A firm yellow, orange, or brown nodule deep in the skin (such as around the Achilles tendon, elbows, or knees) or mucous membrane caused by fat deposition. Although xanthomas themselves are harmless, they frequently indicate underlying disease, such as diabetes, lipid disorders (such as elevated blood cholesterol levels), or other conditions. They are composed…

xanthoma, diabetic Xanthoma that is associated with poorly controlled diabetes mellitus. Treating the diabetes causes diabetic xanthomas to disappear.