title: FISH reanalysis of inner cell mass and trophectoderm samples of previously array-CGH screened blastocysts shows high accuracy of diagnosis and no major diagnostic impact of mosaicism at the blastocyst stage.
abstract: OBJECTIVE
  Does comprehensive chromosome screening (CCS) of cells sampled from the blastocyst trophectoderm (TE) accurately predict the chromosome complement of the inner cell mass (ICM)?
  
  
  CONCLUSIONS
  Comprehensive chromosome screening of a TE sample is unlikely to be confounded by mosaicism and has the potential for high diagnostic accuracy.
  
  
  BACKGROUND
  The effectiveness of chromosome aneuploidy screening is limited by the technologies available and chromosome mosaicism in the embryo. Combined with improving methods for cryopreservation and blastocyst culture, TE biopsy and CCS is considered to be a promising approach to select diploid embryos for transfer.
  
  
  METHODS
  The study was performed between January 2011 and August 2011. In the first part, a new ICM isolation method was developed and tested on 20 good morphology blastocysts. In the main phase of the study, fluorescence in situ hybridization (FISH) was used to reanalyse the ICMs and TEs separated from 70 embryos obtained from 26 patients undergoing blastocyst stage array comparative genome hybridization (aCGH) PGS cycles.
  
  
  METHODS
  The isolated ICM and TE fractions were characterized by immunostaining for KRT18. Then, non-transferrable cryopreserved embryos were selected for the FISH reanalysis based on previous genetic diagnosis obtained by TE aCGH analysis. Blastocysts either diploid for chromosome copy number (20) or diagnosed as single- (40) or double aneuploid (10) were included after preparing the embryo into one ICM and three equal-sized TE sections. Accuracy of the aCGH was measured based on FISH reanalysis. Chromosomal segregations resulting in diploid/aneuploid mosaicism were classified as 'low-', 'medium-' and 'high-' grade and categorized with respect to their distribution (1TE, 2TE, 3TE, ICM or ALL embryo). Linear regression model was used to test the relationship between the distributions and the proportion of aneuploid cells across the four embryo sections. Fisher's exact test was used to test for random allocation of aneuploid cells between TE and ICM.
  
  
  RESULTS
  All ICM biopsy procedures displayed ICM cells in the recovered fraction with a mean number of ICM cells of 26.2 and a mean TE cell contamination rate of 2%. By FISH reanalysis of previously aCGH-screened blastocysts, a total of 66 aneuploidies were scored, 52 (78.8%) observed in all cells and 14 (21.2%) mosaic. Overall, mosaic chromosomal errors were observed only in 11 out of 70 blastocysts (15.7%) but only 2 cases were classified as mosaic diploid/aneuploid (2.9%). Sensitivity and specificity of aCGH on TE clinical biopsies were 98.0 and 100% per embryo and 95.2 and 99.8% per chromosome, respectively. Linear regression analysis performed on the 11 mosaic diploid/aneuploid chromosomal segregations showed a significant positive correlation between the distribution and the proportion of aneuploid cells across the four-blastocyst sections (P < 0.01). In addition, regression analysis revealed that both the grade and the distribution of mosaic abnormal cells were significantly correlated with the likelihood of being diagnosed by aCGH performed on clinical TE biopsies (P = 0.019 and P < 0.01, respectively). Fisher's exact test for the 66 aneuploidies recorded showed no preferential allocation of abnormal cells between ICM and TE (P = 0.33).
  
  
  CONCLUSIONS
  The study is limited to non-transferable embryos, reanalyzed for only nine chromosomes and excludes segmental imbalance and uniparental disomy. The prevalence of aneuploidy in the study group is likely to be higher than in the general population of clinical PGD embryos.
  
  
  CONCLUSIONS
  This study showed high accuracy of diagnosis achievable during blastocyst stage PGS cycles coupled with 24-chromosomes molecular karyotyping analysis. The new ICM isolation strategy developed may open new possibilities for basic research in embryology and for clinical grade derivation of human embryonic stem cells.
  
  
  BACKGROUND
  No specific funding was sought or obtained for this study.
authors.affiliation: GENERA, Centre for Reproductive Medicine, Clinica Valle Giulia, Via G. De Notaris 2b, Rome 00197, Italy. capalbo@generaroma.it
authors.forename: Antonio
authors.initials: A
authors.lastname: Capalbo
authors.forename: Graham
authors.initials: G
authors.lastname: Wright
authors.forename: Thomas
authors.initials: T
authors.lastname: Elliott
authors.forename: Filippo Maria
authors.initials: FM
authors.lastname: Ubaldi
authors.forename: Laura
authors.initials: L
authors.lastname: Rienzi
authors.forename: Zsolt Peter
authors.initials: ZP
authors.lastname: Nagy
mesh_terms: D053624:Blastocyst Inner Cell Mass; D025063:Chromosome Disorders / Q000175:diagnosis; D055028:Comparative Genomic Hybridization / Q000379:methods; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D009030:Mosaicism; D019836:Preimplantation Diagnosis / Q000379:methods*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
keywords: blastocyst mosaicism; embryo aneuploidies; inner cell mass isolation; preimplantation genetic screening; trophectoderm