Altered segregation pattern and numerical chromosome abnormalities interrelate in spermatozoa from Robertsonian translocation carriers.

The aim of this study was to assess whether there is a relationship between numerical chromosome abnormalities and certain segregation modes in spermatozoa from Robertsonian translocation carriers. A sequential fluorescence in-situ hybridization protocol based on two successive hybridization rounds was performed on sperm samples from one t(13;22) and ten t(13;14) carriers. Patient inclusion criteria included the presence of a positive interchromosomal effect (ICE). In the first round, numerical abnormalities for chromosomes 15/22, 18, 21, X and Y were analysed. In the second round, the segregation outcome of the rearranged chromosomes was evaluated in the numerically abnormal spermatozoa detected in the first round, as well as in randomly assessed spermatozoa. Aneuploid spermatozoa showed statistical differences in all segregation modes when compared with randomly assessed spermatozoa: alternate (50.7% versus 84.3%), adjacent (36.6% versus 14.6%) and 3:0 (10.2% versus 1%). Diploid/multiple disomic spermatozoa showed differences in alternate (3.7% versus 84.3%) and 3:0 (67.6% versus 1%). We concluded that in Robertsonian translocation carriers that exhibit ICE, numerically abnormal spermatozoa preferentially contain unbalanced segregation products. This might be explained by heterosynapsis acting as a rescue mechanism that would lead to aberrant recombination, which is a predisposing factor for non-disjunction events.

Karyomapping allows preimplantation genetic diagnosis of a de-novo deletion undetectable using conventional PGD technology.

Preimplantation genetic diagnosis (PGD) was carried out for a couple carrying a de-novo deletion in the TSC2 gene, responsible for tuberous sclerosis. Karyomapping, a method employing genome-wide analysis of single nucleotide polymorphisms (SNP), was used as PGD protocol. Analysis of DNA from the affected parent using karyomapping confirmed the region covered by the deletion and revealed more than 30 SNP located within the affected region. These SNP were subsequently used for embryo diagnosis (deletion revealed by hemizygosity and/or reduced probe intensity). Seven blastocyst embryos underwent trophectoderm biopsy followed by vitrification. Biopsied cells were subjected to comprehensive aneuploidy screening using microarray comparative genomic hybridization (aCGH), with karyomapping for the detection of embryos carrying the mutant TSC2 gene carried out in tandem. Two embryo transfers were performed, the second of which resulted in the birth of a child. This study highlights that karyomapping may be applicable to a subset of de-novo mutations undetectable using standard PGD strategies. Additionally, karyomapping results were in complete concordance with aCGH, both methods revealing the same aneuploidies in the embryos tested. It was concluded that karyomapping may represent a valuable advance in cases of PGD for monogenic diseases.