Disease relevance of XG

• Histiocytosis X is characterized by the presence of cytoplasmic rod structures called Langerhans' cell granules or X granules (XG) [1].
• Hypogammaglobulinaemia and measles pneumonitis had preceded infection with E.B.V. The diverse phenotypic expressions probably resulted from the varied immune response to E.B.V. Recombination of X chromosomes was documented by Xg-blood-group studies in a survivor [2].
• The Xg blood group antigen (a genetic marker of a region of the X chromosome at a considerable distance from protan/deutan color blindness) was studied for linkage to bipolar manic-depressive illness [3].
• At least two instances of recombination between Xg blood-group and Lowe syndrome loci [4].
• Results of studies of the Xg blood group excluded close linkage between the optic atrophy and Xg genes [5].

Psychiatry related information on XG

• Linkage studies in affective disorders: the Xg blood group and manic-depressive illness [6].

High impact information on XG

• Cloning of PBDX, an MIC2-related gene that spans the pseudoautosomal boundary on chromosome Xp [7].
• The Xg blood-group locus and the G6PD locus were determined in these six individuals [4].
• RT-PCR analysis of the transcripts revealed the existence of an XG mRNA in each cell line, suggesting that the tissue-specific regulation of cell surface XG expression occurs either at a quantitative transcriptional level or is a posttranscriptional event [8].
• A study of the coregulation and tissue specificity of XG and MIC2 gene expression in eukaryotic cells [8].
• No evidence of association or complex formation between XG and CD99 proteins could be proven, either on transfected RAG cells or on human erythrocytes [8].

Biological context of XG

• The three exons at the 5' end of PBDX are situated in the pseudoautosomal region immediately downstream of MIC2, whereas the other seven exons are in the X-specific region [7].
• An expressed pseudogene of XG, XGPY, has been mapped to interval Yq11.21 [9].
• Sequence comparison suggests that XGPY originated from XG by a gene duplication event in the primate lineage [9].
• The heterogeneity and low abundance of transcripts as well as the lack of maintenance of the XG open reading frame in all but one transcript argue against a specific Y-chromosome gene product [9].
• The XG blood group gene spans PABX1, the pseudoautosomal boundary on the X chromosome [9].

Anatomical context of XG

• The percentage of histiocytes with XG in a lesion has no relation to the age of the patient or the organ from which it was obtained, except for skin, where they were quite numerous [1].
• Although no explanation has been established for the presence of testes in the apparent absence of the Y chromosome, studies of the X-linked Xg blood group in XX males demonstrate a high frequency of unusual inheritance patterns [10].

Other interactions of XG

• These findings suggest that the phenotypic relationship between XG and CD99 is mostly regulated at the transcriptional level, but they do not formally exclude some posttranscriptional effect [8].
• Transcripts detected include antisense SRY sequences and XG approximately RPS4Y hybrid transcripts [9].
• Contrary to what is expected under the above hypothesis, our sequence data from humans and great apes reveal that the PAR1 introns of XG have actually evolved slightly slower than X-specific introns [11].
• This order was 2.4 times more likely than with (STS,GMGX9) and dic56 reversed and is supported by our findings in a male with steroid sulfatase deficiency due to a deletion of Xp22.3 which encompasses the XG locus [12].

Analytical, diagnostic and therapeutic context of XG

• By Northern blot analysis, XG transcripts were detected in erythroid tissues and several nonerythroid tissues [8].
• As a preliminary study of this phenomenon, human XG and CD99 recombinant proteins were expressed in murine RAG cells and analyzed by flow cytometry [8].

References