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Topic: Lyonization

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	X-Chromosome inactivation in healthy females: incidence of excessive lyonization with age and comparison of assays ...
		X-Chromosome inactivation in healthy females: incidence of excessive lyonization with age and comparison of assays involving DNA methylation and transcript polymorphisms -- El Kassar et al.
		In females with nonrandom lyonization or patients with clonal hematopoiesis, one peak of 21 or 24 bases was detected in T or C polymorphism respectively, while two peaks were detected in cases of random X-lyonization.
		In heterozygous females with nonrandom lyonization or in patients with clonal hematopoiesis, one peak (in addition to the peak corresponding to fluorescent primer) is detected, while two peaks are detected in cases with random X-inactivation.
	www.clinchem.org /cgi/content/full/44/1/61 (3460 words)

	NYU SoM Neurology - Fabry Disease Program
		Lyonization refers to the random inactivation of one of the two X chromosomes that occurs early on in the development of female cells.
		Diseases that are passed on in an X-linked recessive fashion are primarily expressed in males because of the absence of a corresponding normal copy from another X chromosome (as seen in females) that would have made up for the deficiency.
		All female children born to an affected male individual are carriers of the trait; as affected males pass on their Y chromosome to their sons, none of their male children will have the disease.
	www.med.nyu.edu /neurology/subspecialties/neurogenetics/fabry.html (1998 words)

	The Genetics of Calico Cats
		This irreversible process is known as Lyonization; it leaves only ONE active X chromosome in each cell of the female embryo.
		Lyonization is random in each cell: there's no way to predict which of the two X chromosomes will become inactivated.
		Lyonization takes place relatively early in development, when the cat is still a blastula, and all the cells descended from a blastomere with a particular X chromosome inactivated as a Barr Body will also have the same Barr Body inactivated.
	www.bio.miami.edu /dana/dox/calico.html (916 words)

	PMID: 3513574 (Site not responding. Last check: 2007-10-26)
		We hypothesize a maternal effect in fra(X), with variability in intelligence of heterozygotes and hemizygotes mediated mainly by the maternal uterus or placenta by virtue of different patterns of lyonization in those tissues between pregnancies.
		Modifiers of the intrauterine effect could include lyonization patterns in tissues of the carrier fetus, and preferential inactivation of the paternal X in extra-embryonic tissues.
		The ultimate phenotype of the developing heterozygote and hemizygote may be determined by a threshold effect and interaction between the maternal genotype, the placental genotype, and the fetal genotype.
	lethargy.swmed.edu /cgi-bin/etblast/abstract_local?pmid=3513574&user_id=1015821415&application=0 (265 words)

	Case Based Pediatrics Chapter
		However, because of random inactivation of one of the X chromosomes in females (a phenomenon known as Lyonization), there is a remote possibility for the normal allele to be inactivated in most cells, thereby permitting full phenotypic expression.
		Lyonization (X chromosome inactivation): Females have two X chromosomes while males have only one.
		Certain data suggest that the major reason for Lyonization is "dosage compensation"-making certain that the same levels of proteins and enzymes are expressed in males and females.
	www.hawaii.edu /medicine/pediatrics/pedtext/s04c07.html (3931 words)

	X Chromosome
		During the early stages of the embryonic development of a female, one of the two x chromosomes is permanently (but randomly) shut down or turned off in the somatic cells.
		This process is called the X-inactivation or Lyonization.
		This process of turning off the extra X chromosome is performed by the body to make sure that females, along with males, will only have one working copy of the X chromosome in their cells.
	www.iscid.org /encyclopedia/X_Chromosome (281 words)

	Genetics
		Lyon hypothesis (lyonization) - one X-chromosome active, the other inactivated; X-inactivation occurs early in embryonic development; inactive X-chromosome can be maternal or paternal in origin, choice of X-chromosome to be inactivated is random with respect to origin and independent of choice of other embryonic cells; X-inactivation is irreversible in somatic cell and remains so
		Nonrandom (skewed) X-inactivation (lyonization) - during early embryonic development in somatic cells of female one X chromosome is nonrandomly inactivated
		X-inactivation (lyonization) - during early embryonic development in somatic cells of female one X chromosome is randomly inactivated
	www.siu.edu /departments/biochem/som_pbl/CRR/genetics.html (528 words)

	Genetics
		Lyon hypothesis (lyonization) - one X-chromosome active, the other inactivated; X-inactivation occurs early in embryonic development; inactive X-chromosome can be maternal or paternal in origin, choice of X-chromosome to be inactivated is random with respect to origin and independent of choice of other embryonic cells; X-inactivation is irreversible in somatic cell and remains so
		Nonrandom (skewed) X-inactivation (lyonization) - during early embryonic development in somatic cells of female one X chromosome is nonrandomly inactivated
		X-inactivation (lyonization) - during early embryonic development in somatic cells of female one X chromosome is randomly inactivated
	www.siumed.edu /~eniederhoffer/som_pbl/CRR/genetics.html (528 words)

	Highbeam Encyclopedia - Search Results for Lyonization
		Anions can be formed from nonmetals by reduction (see oxidation and reduction) or from neutral acids (see acids and bases) or polar compounds by ionization.
		Find newspaper and magazine articles plus images and maps related to "Lyonization" at HighBeam.
		A genetic study of familial hypophosphatemia and vitamin D resistant rickets with a review of the literature.
	www.encyclopedia.com /SearchResults.aspx?Q=Lyonization&StartAt=1 (569 words)

	BioEd Online Slides: Lyonization, X chromosome, silencers, promoters
		During X-inactivation, most genes on one of the X chromosomes of a female are inactivated in a mechanism that provides dosage compensation to equalize the level of gene expression of most X-linked genes in females to that of males who have only one X chromosome.
		This process, often called Lyonization, results in the formation of a Barr body, the highly compacted, inactive X chromosome.
		X-inactivation, sometimes called Lyonization, occurs during embryogenesis and is the process by which most genes on one of the X chromosomes of a female are inactivated.
	www.bioedonline.org /slides/slide01.cfm?q=Lyonization (767 words)

	Helath reference website providing news articles directory internet search.
		The classic reaction to consumption of broad beans has led to the commonly used term favism, derived from the Italian name of the broad bean (fava).
		Patients are almost exclusively male, due to the X-linked pattern of inheritance, but female carriers can be clinically affected due to lyonization where random inactivation of an X-chromosome in certain cells creates a population of G6PD deficient red cells coexisting with normal red cells.
		Although female carriers can have a mild form of G6PD (dependent on the degree of inactivation of the unaffected X chromosome - see lyonization), homozygous females have been described; in these females there is co-incidence of a rare immune disorder termed chronic granulomatous disease (CGD).
	www.medconsultants.eu /Glucose-6-phosphate-dehydrogenase-deficiency.php (926 words)

	[No title] (Site not responding. Last check: 2007-10-26)
		Miles (Unproofed) Mendelian Inheritance (Classic) Equivalence of reciprocal crosses: Does not matter if gene is inherited from your mother or your father.
		Mosaicism Condition in which there are two or more cell lines, derived from a single zygote but differing genetically because of post-zygotic mutation, non-disjunction, or lyonization.
		Example cited in lecture were “Lines of Blaschko” which look like zebra striping and are the result of the migration of different epidermal cell lines during development.
	www.muhealth.org /~md2004/update5/9-04nonmendelian.doc (1214 words)

	Journal of Investigative Dermatology - Mosaic Pattern of Maternal and Paternal Keratinocyte Clones in Normal Human ... (Site not responding. Last check: 2007-10-26)
		A pattern of X-chromosome inactivation "tiles" is established in epidermis.
		The structure depends on when during embryogenesis lyonization occurs and the extent to which stem cells are mixed during migration.
		Although the mosaic pattern in the epidermis is determined during embryogenesis, it may change with age and exposure to ultraviolet light.
	www.nature.com /jid/journal/v117/n1/full/5601126a.html (4021 words)

	GeneDx :: Tests :: Androgen Insensitivity Syndrome, Testicular Feminization Syndrome
		In the partial form, patients may exhibit hypospadias and micropenis, fusion of the labial folds, with the occurrence of virilization at puberty.
		Heterozygous females may exhibit patchy changes in hair distribution and irregular menses, due to skewed Lyonization of the X-chromosome.
		Using genomic DNA obtained from a venous blood sample in EDTA, each of the 8 exons of the AR gene is screened by bi-directional sequence analysis.
	www.genedx.com /services/dis_ais.php (308 words)

	Pigmentary Disorders Academy (Site not responding. Last check: 2007-10-26)
		Hence, it can be taken as certain that the Blaschko-linear pattern of X-linked pigmentary disorders reflects the action of retrotransposons.
		Lyonization can give rise to 3 distinct mosaic patterns.
		It should be kept in mind, however, that some X-linked genes escape lyonization.
	www.pigmentarydisordersacademy.org /PigmentaryMosaicismMechanisms.jsp (2042 words)

	UpToDate Diagnosis and treatment of glucose-6-phosphate dehydrogenase deficiency
		However, the mean red blood cell enzyme activity in heterozygous females may be normal, moderately reduced, or grossly deficient depending upon the degree of lyonization and the degree to which the abnormal G6PD variant is expressed [3].
		A female with 50 percent normal G6PD activity, due to inactivation of one X chromosome in each cell via lyonization, has 50 percent normal red cells and 50 percent G6PD-deficient red cells.
		The deficient cells are as vulnerable to hemolysis as the enzyme-deficient red blood cells in males.
	patients.uptodate.com /topic.asp?file=red_cell/21725&title=Jaundice (630 words)

	Fragile X Syndrome (Site not responding. Last check: 2007-10-26)
		Since an organ (e.g., the liver) originates from a small cluster of cells, by chance alone, a large number of the cells within the organ could have a normal functioning X (or an abnormal functioning X).
		Thus, X chromosome inactivation, or lyonization, creates normal cells and abnormal cells depending on whether the normal X or the abnormal X is active, on average, 50% of each.
		Thus lyonization can modify the expression of abnormal genes, whether dominant or recessive, on the X chromosomes in females.
	www.msu.edu /user/sweeley/frax (748 words)

	Coagulation Disorders in Pregnancy- New Treatments, January 2, 2007
		The next inherited bleeding disorder is hemophilia A; this is an X-linked recessive disorder in one in ten thousand white males.
		If you remember, lyonization is when one X chromosome gets inactivated.
		If there is a disproportionate inactivation of the normal X chromosome, you can have a female with hemophilia A. Clinically, then experience bruising, muscle hematomas and hemarthrosis.
	www.ccspublishing.com /journals5a/coagulation_disorders.htm (1691 words)

	NDI Article: 71 (Site not responding. Last check: 2007-10-26)
		In contrast, the mother acts as an NDI patient when the urine concentration is measured, but acts as a carrier in terms of the factor VIII response to desmopressin.
		From the earliest reports on congenital vasopressin-resistant diabetes insipidus (NDI) in man, researchers have emphasized that the vast majority of cases occur in males and are transmitted in an X-linked recessive manner (1-3).
		We propose that in the case of the mother, renal tubular cells underwent the well characterized phenomenon of extreme lyonization of X-chromosome inactivation, which has recently been reviewed in patients with X-linked disease states (24-29).
	www.ndif.org /Article/jar-71.html (1887 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal (Site not responding. Last check: 2007-10-26)
		The classic reaction to consumption of broad beans has led to the commonly used term favism, derived from the Italian name of the broad bean (fava).
		Patients are almost exclusively male, due to the X-linked pattern of inheritance, but female carriers can be clinically affected due to lyonization where random inactivation of an X-chromosome in certain cells creates a population of G6PD deficient red cells coexisting with normal red cells.
		Although female carriers can have a mild form of G6PD (dependent on the degree of inactivation of the unaffected X chromosome - see lyonization), homozygous females have been described; in these females there is co-incidence of a rare immune disorder termed chronic granulomatous disease (CGD).
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=Glucose-6-phosphate_dehydrogenase_deficiency (936 words)

	Infectious Diseases in Children
		This case turned out to be incontinentia pigmenti (IP), an X-linked dominant disorder with mortality in males, also known as Bloch-Sulzberger syndrome.
		Variable presentation among patients is thought to be due to Lyonization.
		The term IP describes the histologic feature where there is incontinence of the melanocytes in the basal layer of the epidermis into the superficial dermis.
	idinchildren.com /200104/WYD.asp (1434 words)

	X-linked recessive disorders - General Practice Notebook (Site not responding. Last check: 2007-10-26)
		only rarely will a female manifest the signs of an X-linked disease; this is usually due to atypical lyonization, a new mutation in the other X chromosome, a carrier with Turner's syndrome, or X-autosome translocation
		milder signs of X-linked disorders may evolve in the female due to normal lyonization
		Approximately 290 X-linked recessive conditions are known, the following are the most frequently encountered:
	www.gpnotebook.co.uk /cache/-1341784030.htm (153 words)

	Cecil Textbook of Medicine : />
		Female carriers transmit the coagulation disorder to half of their sons, whereas half of their daughters become carriers.
		Female carriers can manifest hemophilia-like symptoms when the alleles on the X chromosome are unequally inactivated (lyonization); the defective hemophilic allele is expressed in preference to the normal allele, and a phenotypic hemophiliac is produced.
		Female hemophilia can arise as the result of mating between a hemophilic male and a female carrier (homozygous for the defective factor VIII or IX gene) or in carrier females who have the 45 XO karyotype (Turner's syndrome) (hemizygous for the defective hemophilia gene).
	www.merckmedicus.com /ppdocs/us/common/cecils/chapters/178_005.htm (432 words)

	Re: If one of X chromosomes is Barr-body, why aren't more women color blind?
		Your question is an interesting one, and deals with the process of "Lyonization" or inactivation of one of the X chromosomes in women.
		There have been studies (see reference below) suggesting subtle differences in color vision between women with only one normal gene for red/green vision, as opposed to women with two normal copies of the gene.
		Research labs have looked at the inactivation of X- linked genes in these women, and found that (in many of them) ~90% or more of the cells in their body have inactivated the X chromosome carrying the "normal" copy of the factor VIII gene.
	www.madsci.org /posts/archives/oct99/941146113.Ge.r.html (368 words)

	[No title]
		Your search - "lyonization" - did not match any HowStuffWorks documents.
		X-inactivation (also called lyonization) is a process by which one of the two
		Lyonization definition - Medical Dictionary definitions of popular...
	www.howstuffworks.com /search2.php?pg=&server=www.howstuffworks.com&terms=lyonization (119 words)

	Mary F. Lyon Summary
		The identification of this structure used to form the basis of gender identification tests in athletic competitions, as males lack a Barr body.
		The verification of the Lyon Hypothesis has afforded crucial insight into the processes and evolution of sexual differentiation and made "Lyonization" a model system for the study of how cells read their genetic code.
		Among her awards and honors are the Royal Medal of the Royal Society and the Wolf Prize in Medicine.
	www.bookrags.com /Mary_F._Lyon (564 words)

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