U‐type exchange in a paracentric inversion as a possible mechanism of origin of an inverted tandem duplication of chromosome 8

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Abstract
A mentally retarded male with dysmorphic features was found to have a de novo 46,XY,inv dup(8) (p.23.1 → 12). Confirmation of the segments duplicated in the rearrangement was achieved by biochemical analysis of glutathione reductase, which maps to 8p21.1, and DNA studies using the chromosome specific probe y‐19‐1D (D85131), which maps to 8p21. Assay of cathepsin B, which has been localised to 8p22, did not differ from controls with normal chromosomal constitution. DNA studies using the Defensin 1 gene probe, which maps to 8p23, showed a previously undetected deletion of that segment. We propose that the inverted tandem duplication/deletion arose as a single U‐type exchange within an inversion loop.