X chromosome

About: X chromosome is a research topic. Over the lifetime, 9862 publications have been published within this topic receiving 407354 citations. The topic is also known as: GO:0000805 & chrX.

Clonality in myeloproliferative disorders: analysis by means of the polymerase chain reaction.

Abstract: The myeloproliferative syndromes are acquired disorders of hematopoiesis that provide insights into the transition from somatic cell mutation to neoplasia. The clonal origin of specific blood cells can be assessed in patients with X chromosome-linked polymorphisms, taking advantage of random inactivation of the X chromosome. We have adapted the PCR for determination of clonality on as few as 100 cells, including individual colonies grown in culture. Amplifying a polymorphic portion of the X chromosome-linked phosphoglycerate kinase (PGK) gene after selective digestion of the active X chromosome with a methylation-sensitive restriction enzyme gave results fully concordant with standard Southern blotting of DNA samples from normal (polyclonal) polymorphonuclear cells (PMN) as well as clonal PMN from patients with myelodysplastic syndrome and polycythemia vera (PCV). We have used this technique to demonstrate heterogeneity of lineage involvement in patients with PCV. The same clinical phenotype may arise from clonal proliferation of different hematopoietic progenitors.

Identification of FMR2, a novel gene associated with the FRAXE CCG repeat and CpG island.

Abstract: Five folate-sensitive fragile sites have been identi-fied at the molecular level to date1–8. Each is characterized by an expanded and methylated trinucleotide repeat of CGG (CCG). Of the three X chromosome sites, FRAXA, FRAXE and FRAXF, the former two are associated with mental retar-dation in their expanded forms. FRAXA expansion results in fragile X syndrome due to down regula-tion of expression of the FMR1 gene, which carries the hypermutable CGG repeat in the 5′ untranslated portion of its first exon9,10. Mild mental retardation without ponsistent physical findings has been found associated with expanded CCG repeats at FRAXE11–13. We have identified a large gene (FMR2) transcribed distally from the CpG island at FRAXE, and down-regulated by repeat expansion and methylation. The gene is novel, expressed in adult brain and placenta, and shows similarity with another human protein, MLLT2, expressed from a gene at chromosome 4q21 involved in translocations found in acute lymphoblastic leukaemia (ALL) cells14,15. Identifi-cation of this gene will facilitate further studies to determine the role of its product in FRAXE associated mental deficiency.

Contiguous gene syndromes due to deletions in the distal short arm of the human X chromosome.

Abstract: Mendelian inherited disorders due to deletions of adjacent genes on a chromosome have been described as "contiguous gene syndromes." Short stature, chondrodysplasia punctata, mental retardation, steroid sulfatase deficiency, and Kallmann syndrome have been found as isolated entities or associated in various combinations in 27 patients with interstitial and terminal deletions involving the distal short arm of the X chromosome. The use of cDNA and genomic probes from the Xp22-pter region allowed us to identify 12 different deletion intervals and to confirm, and further refine, the chromosomal assignment of X-linked recessive chondrodysplasia punctata and Kallmann syndrome genes. A putative pseudoautosomal gene affecting height and an X-linked non-specific mental retardation gene have been tentatively assigned to specific intervals. The deletion panel described is a useful tool for mapping new sequences and orienting chromosome walks in the region.