Fragile X expression and X inactivation. I. The expression of the fragile site at Xq27.3 is not suppressed on inactive X chromosomes separated from the active homologue.
The inactive fragile X chromosomes of a 47,fra(X),fra(X),Y male with a typical fragile X phenotype were successfully separated from the active homologues by means of somatic cell hybridization. It was shown by FUdR-induction and caffein-posttreatment that the separated inactive X chromosomes expressed their fragile sites and that the presence of an active mutated X chromosome was not a prerequisite for fragile X expression. The fragility seems to be an intrinsic property of the individual fragile site. This result is in favour of the classical concept that the fragile site at Xq27.3 has a primary pathogenetic function in this syndrome, although the fragility itself could represent a secondary phenomenon related to an unknown alteration of the DNA in this chromosome region. It is also concluded that inactivation of the fragile X chromosome in females is not responsible for either false negative fragile X findings or the observation of fragile X negative colonies isolated from fragile X positive fibroblasts in heterozygotes.
Wöhrle
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Abteilung Klinische Genetik der Universität, Ulm, Federal Republic of Germany.
Fryns
J P
JP
Steinbach
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P
D002871:Chromosome Banding; D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility; D015342:DNA Probes; D004303:Dosage Compensation, Genetic; D005600:Fragile X Syndrome / Q000235:genetics*; D015870:Gene Expression; D006801:Humans; D006822:Hybrid Cells; D008607:Intellectual Disability / Q000235:genetics; D007713:Klinefelter Syndrome / Q000235:genetics; D008297:Male
D015342:DNA Probes