Lack of meiotic crossovers during oogenesis in an apparent 45,X Ullrich-Turner syndrome patient with three children.

A woman with apparent 45,X Ullrich-Turner syndrome was ascertained after the birth of three girls, the last being growth retarded due to a del(X)(p22.11) of grand-paternal origin. In this woman no del(X)-chromosome was detectable in blood by FISH or PCR. Fibroblast cultures from four different biopsies of her skin varied from having 45,X only to mosaic 46,X,del(X) to 46,X,del(X) only. In one fibroblast culture, a few cells with two del(X) chromosomes were found, probably remnants of a paternal dicentric X that caused the condition. Her three daughters were born when she was 29, 31, and 39 years old, respectively, indicating that disomy for the distal half of Xp is not required for normal folliculogenesis. When studying the crossover pattern of her daughters' maternal X-chromosomes, it turned out that one daughter had an X that was exclusively grand-maternal, one daughter lacked crossovers on Xq, and one daughter lacked crossovers on Xp. This suggests that univalent X-chromosomes were present in the Ullrich-Turner patient's primordial egg cells, either because there was only a single X-chromosome present (a 45,X primary oocyte), or because the X-chromosome was a partially or completely unpaired in pachytene, indicating a problem with chromosome association and synapsis formation.