Numerical sex chromosome abnormalities were analyzed in sperm from four fathers of Turner syndrome patients of paternal origin to determine whether there was an increased frequency of sex chromosome aneuploidy and to elucidate whether meiotic malsegregation mechanisms could be involved in the origin of Turner syndrome. Determination of the parental origin of the single X chromosome (maternal in all four cases) and exclusion of X and Y mosaicism were carried out by polymerase chain reaction amplification of five X chromosome polymorphisms and three Y chromosome segments. A total of 45,299 sperm nuclei from Turner fathers and 85,423 sperm nuclei from eight control donors was analyzed by three-color fluorescence in situ hybridization. The four patients showed a significant increase in the percentages of XY sperm (mean 0.22%; range 0.20% to 0.22%) compared with control donors (mean 0.11%; range 0.06% to 0.18%). These results suggest that the four individuals have an increased frequency of nondisjunctional errors in meiosis I, resulting in the production of an increased proportion of XY spermatozoa and of sperm lacking a sex chromosome.

The aim of this study was to determine if donor age is associated with an increased incidence of diploidy and of disomy for the sex chromosomes and for chromosomes 6 and 21. We used simultaneous fluorescence in situ hybridisation (FISH) for chromosomes 6, 21, X and Y in sperm from 18 healthy donors, aged 24 ± 74 years (mean 48.8 years). A total of 194 024 sperm were analysed, with a minimum of 10 000 sperm scored for each donor. Our results indicate a significant increase of the level of diploidy (P=0.002), and a marginal significance of total sex chromosome disomy (P=0.055) with age. No increase was observed for disomies XX, YY, XY, 21 or 6. The percentages of increase for disomy and for diploidy ranged from 0.3 to 17% for each 10-year period. Chromosomes 6 and 21 did not segregate preferentially with the X or Y chromosomes. Our findings show a linear trend association between age and diploidy in human males.

Analysis of sperm karyotypes and two-color fluorescent in situ hybridization (FISH) on sperm nuclei were carried out in a man heterozygous for the pericentric inversion inv(9)(p11q13). Sperm chromosome complements were obtained after in vitro fusion of zona-free hamster oocytes and donor sperm. A total of 314 sperm complements was analyzed: 153 (48.7%) carried the inverted chromosome 9 and 161 (51.3%) carried the normal one. None of the sperm complements contained a recombinant chromosome 9, suggesting that no chiasmata were formed in the heterochromatic region. The frequency of structural chromosome aberrations unrelated to the inversion (8.3%) and the frequency of conservative aneuploidy (3.2%) were within the limits observed in our control donors. The proportions of X-bearing (47.3%) and Y-bearing sperm (52.7%) were not significantly different from the expected 1:1 ratio. The percentage of disomy for chromosome 21 was analyzed by two-color FISH in 10336 sperm nuclei. The disomy rate for chromosome 21 (0.30%) was not significantly different from that found in our controls. These results suggest that the risk for this man of producing chromosomally abnormal offspring or spontaneous abortions was not increased, and do not support the existence of an interchromosomal effect for chromosome 21.

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.

Preimplantation genetic diagnosis (PGD) has been applied worldwide for a great variety of single-gene disorders over the last 20 years. The aim of this work was to perform a double-factor preimplantation genetic diagnosis (DF-PGD) protocol in a family at risk for Lynch syndrome. The family underwent a DF-PGD approach in which two blastomeres from each cleavage-stage embryo were biopsied and used for monogenic and comprehensive cytogenetic analysis, respectively. Fourteen embryos were biopsied for the monogenic disease and after multiple displacement amplification (MDA), 12 embryos were diagnosed; 5 being non-affected and 7 affected by the disease. Thirteen were biopsied to perform the aneuploidy screening by short-comparative genomic hybridization (CGH). The improved DF-PGD approach permitted the selection of not only healthy but also euploid embryos for transfer. This has been the first time a double analysis of embryos has been performed in a family affected by Lynch syndrome, resulting in the birth of two healthy children. The protocol described in this work offers a reliable alternative for single-gene disorder assessment together with a comprehensive aneuploidy screening of the embryos that may increase the chances of pregnancy and birth of transferred embryos.