Skip to Content

Are you based in North America? If yes, switch to our North American website →


Catalogue Numbers
LPU 018 (10 tests)
LPU 018-S (5 tests)

In humans, one X chromosome is inactivated (Xi) in every female cell in order to achieve transcriptional balance. An X-linked inactivation centre (XIC) is responsible for the initiation of X inactivation.

The exact size of the XIC is unclear but it includes the X-inactive specific transcript (XIST) gene at Xq13.2. This encodes a large non-coding RNA that is initially expressed on both X chromosomes before ceasing expression on the active X and becoming upregulated on the X that is to become inactivated1. The XIST RNA product coats the future Xi chromosome, spreading out from the XIC.

Very small ring r(X) chromosomes that do not include the XIST gene have been associated with a more severe phenotype in syndromes such as Turner Syndrome2,3.


1. Boumil RM, Lee JT et al., Hum Mol Genet 2001;10(20):2225-32

2. Le Caignec C et al., Prenat Diagn 2003;23(2):143-5

3. Bouayed Abdelmoula N, Ann Genet 2004;47(3):305-13

Microscope Images

XIST magnified


This product is intended to be used on Carnoy’s solution (3:1 methanol/acetic acid) fixed peripheral blood samples.