Abnormal Y chromosomes and monosomy 45,X: a concept derived from the study of three patients.

De novo structural rearrangement of the Y chromosome was discovered in one cellular component of a mosaicism in each of three individuals. In each case another cellular component had lost the Y chromosome completely and was monosomic (45,X). Consideration of these three observations, in light of the regularity with which an association has been reported previously, led to the formulation of a concept to explain, in terms of a single disruptive cytogenetic event in the zygote or an early postzygotic cell, the simultaneous derivation of a cell with an abnormal Y and a monosomic sister cell devoid of a Y completely. An intrachromosomal rearrangement affecting the Y is proposed to give rise to one rearranged Y and to one acentric Y fragment. The unlike sister cells derived would be progenitors of two abnormal cellular components of a mosaic embryo. Should the rearrangement occur in a postzygotic cell, a third and normal (46,XY) component would be represented as well.