lyonization


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lyonization

 [li″on-ĭ-za´shun]
the process by which or the condition in which all X chromosomes of the cells in excess of one are inactivated on a random basis.

ly·on·i·za·tion

(lī'on-i-zā'shŭn),
The normal phenomenon that wherever there are two or more haploid sets of X-linked genes in each cell all but one of the genes are inactivated apparently at random and have no phenotypic expression. Lyonization is usual but not invariable for all loci. Its randomness explains the more variable espressivity of X-linked traits in women than in men. Lyonization occurs in men with the Klinefelter (XXY) karyotype.
See also: gene dosage compensation.
[M. Lyon]

lyonization

Genetics A normal genetic event that consists of inactivation of all X chromosomes–portions of the 'inactivated' chromosome may remain functional if in excess of one

ly·on·i·za·tion

(lī'on-ī-zā'shŭn)
The normal phenomenon whereby wherever there are two or more haploid sets of X-linked genes in each cell, all but one of the genes are inactivated apparently at random and have no phenotypic expression. Its randomness explains the more variable expressivity of X-linked traits in women than in men.
See also: gene dosage compensation
Synonym(s): Lyon hypothesis, X-inactivation.
[M. Lyon]

Lyonization

See X-INACTIVATION.

Lyon,

Mary F., English cytogeneticist, 1925–.
Lyon hypothesis - Synonym(s): lyonization
lyonization - the normal phenomenon that wherever there are two or more haploid sets of X-linked genes in each cell, all but one of the genes are inactivated, apparently at random, and have no phenotypic expression. Synonym(s): Lyon hypothesis; X-inactivation
References in periodicals archive ?
Random inactivation of 1 chromosome X in the cells of various tissues and organs (lyonization) explains the phenotypic heterogeneity in females.
However, GLA gene molecular analysis is necessary to confirm the diagnosis in heterozygous females because they express highly variable levels of the enzyme owing to lyonization. (7)
Epigenesis can switch off whole chromosomes (Lyonization) or individual genes (imprinting).
In spite of this limitation, the DHR assay has been successfully used to (a) measure transfused non-CGD neutrophils in CGD patients (9), (b) measure X-inactivation ratios (lyonization patterns) in X-linked CGD carriers (10-16) even when small percentages of the normal X-linked genes are present (17), (c) measure low concentrations of residual NADPH-oxidase activity in CGD patients (10, 18), and (d) measure improved granulocyte activity in preclinical (19) and clinical gene therapy trials (20, 21).
Increased susceptibility of a carrier of X-linked chronic granulomatous disease (CGD) to Aspergillus furnigatus infection associated with age-related skewing of lyonization. Ann Hematol 2001; 80:113-5.
This pattern of inactivation gets transmitted to each daughter cell and is maintained through subsequent cell cycles of proliferation following the principle of "lyonization." (16) Most normal tissues are polyclonal, composed of a mosaic of cells containing random X chromosome inactivation.
The gp91-phox gene is located on the X chromosome, and carriers show a mosaic of nonpathogenic and defective cells, as our patient did, attributable to lyonization. The p22-phox gene is located on chromosome 16g24, and therefore a mosaic of nonpathologic and defective cells is not likely because of a mutation in this gene.
This carrier status, together with an extreme lyonization, appears to explain the clinical phenotype of CGD with severe recurrent infections.
Favorable lyonization may result in a normal pattern of staining in females with X-linked AS.
The mother testing positive according to these criteria may be a carrier having a favorable lyonization pattern because she has never presented clinical symptoms.
However, 21-31% of healthy women have a skewing pattern of X-inactivation (or lyonization) with techniques based on DNA polymorphism, leading to a potential limitation for X-inactivation clonality assays because constitutional skewing mimics clonal derivation of cells, rendering clonality results uninterpretable [7,13].
In addition to biological explanations, technical reasons may account for some of the discrepancies in the estimation of skewed lyonization in healthy females and possibly clonality analysis in various malignancies.