Characterisation, phenotypic manifestations and X-inactivation pattern in 14 patients with X-autosome translocations.

Here we describe a group of 14 patients carrying different X-autosome translocations and exhibiting phenotypes that demonstrate the range of alterations induced by such aberrations. All male carriers of an X-autosome translocation in our investigation group were infertile, whereas fertility in the female carriers was dependent on the position of the break-point in the X chromosome. Fertile women with translocation break-points outside of the critical region (Xq13-q26) in some cases passed on the translocation to their offspring. In balanced female carriers in our group, the normal X chromosome was usually inactivated, allowing full expression of genes on the translocated segments. In one case, disruption of the dystrophine gene in Xp21 led to the manifestation of Duchenne muscular dystrophy in a female carrier. Inactivation of the derivative X (Xt) in a balanced female carrier led to a partial monosomy of the autosome/disomy of the X chromosome and resulted in an aberrant phenotype. In unbalanced carriers, Xt is generally late-replicating/inactive, although failed spreading of inactivation to the autosomal segment often results in a partial trisomy, as evidenced by the case of an unbalanced translocation carrier in our group.