title: The use of arrays in preimplantation genetic diagnosis and screening.
abstract: BACKGROUND
  In preimplantation genetic diagnosis (PGD), polymerase chain reaction has been used to detect monogenic disorders, and in PGD/preimplantation genetic screening (PGS), fluorescence in situ hybridization (FISH) has been used to analyze chromosomes. Ten randomized controlled trials (RCTs) using FISH-based PGS on cleavage-stage embryos and one on blastocyst-stage embryos have shown that PGS does not increase delivery rates. Is the failure of PGS due to a fundamental flaw in the idea, or are the techniques that are being used unable to overcome their own, inherent flaws? Array-based technology allows for analysis of all of the chromosomes. Two types of arrays are being developed for use in PGD; array comparative genomic hybridization (aCGH) and single nucleotide polymorphism-based (SNP) arrays. Each array can determine the number of chromosomes, however, SNP-based arrays can also be used to haplotype the sample.
  
  
  OBJECTIVE
  To describe aCGH and SNP array technology and make suggestions for the future use of arrays in PGD and PGS.
  
  
  CONCLUSIONS
  If array-based testing is going to prove useful, three steps need to be taken: [1] Validation of the array platform on appropriate cell and tissue samples to allow for reliable testing, even at the single-cell level; [2] deciding which embryo stage is the best for biopsy: polar body, cleavage, or blastocyst stage; [3] performing RCTs to show improvement in delivery rates. If RCTs are able to show that array-based testing at the optimal stage for embryo biopsy increases delivery rates, this will be a major step forward for assisted reproductive technology patients around the world.
authors.affiliation: Reader in Human Genetics and Embryology, University College London Centre for Preimplantation Genetics and Diagnosis, Institute for Women's Health, University College London and Centre for Reproductive and Genetic Health, Institute for Women's Health, University College London Hospital, London, United Kingdom. Electronic address: joyce.harper@ucl.ac.uk.
authors.forename: Joyce C
authors.initials: JC
authors.lastname: Harper
authors.affiliation: Preimplantation Genetic Diagnosis, Genetics & IVF Institute, Fairfax, Virginia.
authors.forename: Gary
authors.initials: G
authors.lastname: Harton
mesh_terms: D055028:Comparative Genomic Hybridization / Q000379:methods; D005260:Female; D005820:Genetic Testing / Q000941:ethics / Q000379:methods*; D006801:Humans; D008954:Models, Biological; D020411:Oligonucleotide Array Sequence Analysis / Q000941:ethics / Q000706:statistics & numerical data*; D020641:Polymorphism, Single Nucleotide; D011247:Pregnancy; D019836:Preimplantation Diagnosis / Q000941:ethics / Q000379:methods* / Q000639:trends