Abstract
It is known that X isochromosome (Xqi) is frequently associated with 45,X mosaicism. Of 35 cases with Xqi collected by Ferguson-Smith, 23 cases were mosaic for 45,X/46,XXqi. Cases with 45,X/46,XXqi/47,XXqiXqi are also known. Apparently a structurally abnormal chromosome has a tendency for either anaphase lag or mitotic nondisjunction. With C-banding, two major types of human isochromosome X have been identified, namely Xqi with one C-band and Xqi with two C-bands. Since chromosomes with two centromeres are known to be unstable, it is possible that Xqi's which appear to have only one centromere but have two C-bands are more unstable during mitosis than Xqi with one C-band. We have studied six cases of Xqi. Three showed one C-band; all these were without 45,X mosaicism. The other three cases showed two C-bands and were mosaic (one 45,X/46,XXqi; two 45,X/46,XXqi/47,XXqiXqi-identical twins). Seven other cases of isochromosome Xqi have been reported with C-banding studies. Of these, four showed one C-band with XO mosaicism in two; three demonstrated two C-bands and all three were XO mosaics, thus in a total of 13 cases of Xqi studied with C-banding, seven showed one C-band with XO mosaicism in 2 cases, one of which showed no XO cells in skin fibroblasts; six Xqi's had two C-bands and all were mosaic for 45,X/46,XXqi or 45,X/46,XXqi/47,XXqiXqi. Thus it is evident that Xqi with two C-bands has a greater tendency for anaphase lag or mitotic non-disjunction leading to mosaicism.
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Hsu, L., Paciuc, S., David, K. et al. THE NUMBER OF C-BANDS OF HUMAN ISOCHROMOSOME Xqi AND THEIR REIATIONSHIP TO 45,X MOSAICISM. Pediatr Res 11, 457 (1977). https://doi.org/10.1203/00006450-197704000-00526
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DOI: https://doi.org/10.1203/00006450-197704000-00526