A genetic disorder that causes deafness, white forelock (a frontal white blaze of hair), a difference of color between the iris of one eye and the other (heterochromia iridis), white eye lashes, and wide-set inner corners of the eyes.
The deafness is typically congenital (present at birth), bilateral, profound sensorineural (nerve) deafness. The severity of Waardenburg syndrome (WS) varies and about 40 percent of affected persons escape the deafness. The white forelock may be present at birth. The majority of individuals with WS have the white forelock or early graying of the scalp hair before age 30.
WS is inherited in an autosomal dominant manner in which the heterozygous state (with one copy of the gene) is sufficient to cause the syndrome. The homozygous form of WS with two copies of the gene is a very severe (and fortunately rare) disorder with very severe upper-limb defects that has been called the Klein-Waardenburg syndrome.
The gene for classic WS, symbolized WS1, is on chromosome 2 (in band q35) and is the PAX3 gene which encodes a DNA-binding transcription factor that is expressed in the early embryo. The syndrome is named for a Dutch eye doctor named Petrus Johannes Waardenburg (1886-1979) who first noticed that people with differently colored eyes often had a hearing impairment.
- X inactivation
it is a heritable change in gene function without a change in the sequence of the DNA. X inactivation is not restricted to females. It also occurs in males with Klinefelter syndrome who have more than one X chromosome. The phenomenon of X inactivation is also called lyonization after the English geneticist Mary Lyon (1925-) […]
- X, factor
A coagulation factor, a substance in blood essential to the normal clotting process. Production of factor X takes place in the liver and requires vitamin K. The gene for factor X is located on chromosome 13 and is in band 13q34. The “X” in factor X is the Roman numeral “ten.” (All numbered coagulation factors […]
A gene on the X chromosome that is located on the X chromosome. An X-linked disorder is associated with or caused by a gene on the X chromosome.
High-energy radiation with waves shorter than those of visible light. X-ray is used in low doses to make images that help to diagnose diseases and in high doses to treat cancer.
- X-ray crystallography
The use of X-rays of known wavelength to learn the structure of any crystalline material. Put otherwise, X-ray crystallography is a technology by which the locations of atoms in any crystal can be precisely mapped by looking at the image of the crystal under an X-ray beam. The crystal is placed in the beam of […]