The behavior of sex chromosomes in two human X-autosome translocations: failure of extensive X-inactivation spreading.
Two patients, one adult male and one infant girl, bearing different X-autosome translocations, were studied with cytogenetical, ultrastructural and chromosome-painting techniques. The adult male, is a carrier of a reciprocal, balanced translocation involving the X and #2 chromosomes: 46,Y,t(X;2) (q13;p21). This man showed infertility with spermatogenesis arrest at the spermatocyte stage. Synaptonemal complex analysis at pachytene showed the quadrivalent structure and the putative breakage points. Sex-chromatin condensation did not spread towards the autosomal regions of the quadrivalent. The female infant showed diminished body growth and multiple somatic anomalies. She is a 45,Xp-,t(X;21)(p11;p13) carrier, an unbalanced translocation involving chromosomes X and #21, which leads to a monosomy of almost all Xp. The translocated #21 is practically complete, and its centromere is the active one in the rearranged product. The analysis of interphase nuclei with the X-centromere probe shows that the Xq region of the rearranged chromosome is the late -replicating and inactive element. However, X-inactivation does not spread to the attached #21, as shown by the R-banding pattern. Thus, both in the male adult and in the female infant there is a barrier to the spreading effect of X-chromosome inactivation, which is probably due to different mechanisms.
Solari
A J
AJ
Centro de Investigaciones en Reproducción (CIR), Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, (1121) Buenos Aires, Argentina. ajsolari@mail.retina.ar
Rahn
I M
IM
Ferreyra
M E
ME
Carballo
M A
MA
D000328:Adult; D002675:Child, Preschool; D002891:Chromosomes, Human, Pair 21 / Q000235:genetics* / Q000648:ultrastructure; D004303:Dosage Compensation, Genetic; D005260:Female; D006801:Humans; D008297:Male; D008540:Meiosis; D013090:Spermatocytes / Q000648:ultrastructure; D014178:Translocation, Genetic; D014960:X Chromosome / Q000235:genetics* / Q000648:ultrastructure