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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.

A 23-year-old white woman suffering pycnodysostosis whose parents and five siblings were unaffected was investigated. Chromosomal morphology was normal. Histologic examination of a biopsy specimen obtained from the distal phalanx of the left thumb, corresponding to an area on an x-ray film of osteolysis, showed a fibrous dysplasia-like picture. Kinetic studies of calcium metabolism revealed that exchangeable pool size, turnover, and bone accretion rate were all decreased. Intestinal calcium absorption was investigated simultaneously by a double isotope technique and by deconvolution of the plasmatic specific activity curve of 47Ca given per os. Results obtained by both methods coincided in that values were found to be similarly increased. Endogenous fecal calcium was also determined and revealed a similar increase. Some physiopathological implications of these findings are discussed.