What next for preimplantation genetic screening? High mitotic chromosome instability rate provides the biological basis for the low success rate

Preimplantation genetic screening is being scrutinized, as recent randomized clinical trials failed to observe the expected significant increase in live birth rates following fluorescence in situ hybridization (FISH)-based screening. Although these randomized clinical trials are criticized on their design, skills or premature stop, it is generally believed that well-designed and well-executed randomized clinical trials would resolve the debate about the potential benefit of preimplantation genetic screening. Since FISH can analyze only a limited number of chromosomal loci, some of the embryos transferred might be diagnosed as ‘normal’ but in fact be aneuploid for one or more chromosomes not tested. Hence, genome-wide array comparative genome hybridization screening enabling aneuploidy detection of all chromosomes was thought to be a first step toward a better design. We recently showed array screening indeed enables accurate determination of the copy number state of all chromosomes in a single cell. Surprisingly, however, this genome-wide array screening revealed a much higher frequency and complexity of chromosomal aberrations in early embryos than anticipated, with imbalances in a staggering 90% of all embryos. The mitotic error rate in cleavage stage embryos was proven to be higher than the meiotic aneuploidy rate and as a consequence, the genome of a single blastomere is not representative for the genome of the other cells of the embryo. Hence, potentially viable embryos will be discarded upon screening a single blastomere. This observation provides a biological basis for the failure of the randomized clinical trials to increase baby-take-home rates using FISH on cleavage stage embroys

Preimplantation Genetic Diagnosis for Ornithine Transcarbamylase Deficiency by Simultaneous Analysis of Duplex-nested PCR and Fluorescence In Situ Hybridization : A Case Report

Ornithine transcarbamylase (OTC) deficiency is an X-linked co-dominant disorder. A couple, with a previous history of a neonatal death and a therapeutical termination due to OTC deficiency, was referred to our center for preimplantation genetic diagnosis (PGD). The female partner has a nonsense mutation in the exon 9 of the OTC gene (R320X). We carried out nested polymerase chain reaction (PCR) for R320X mutation and fluorescence in situ hybridization (FISH) for aneuploidy screening. Among a total of 11 embryos, two blastomeres per embryo from 9 embryos were biopsied and analyzed by duplex-nested PCR and FISH, and one blastomere per embryo from 2 embryos by only duplex-nested PCR. As a result of PCR and restriction fragment length polymorphism analysis, four embryos were diagnosed as unaffected embryos having the normal OTC gene. Among these embryos, only one embryo was confirmed as euploidy for chromosome X, Y and 18 by FISH analysis. A single normal embryo was transferred to the mother, yielding an unaffected pregnancy and birth of a healthy boy. Based on our results, PCR for mutation loci and FISH for aneuploidy screening with two blastomeres from an embryo could provide higher accuracy for the selection of genetically and chromosomally normal embryos in the PGD for single gene defects

Can Routine Commercial Cord Blood Banking Be Scientifically and Ethically Justified?

Background to the debate: Umbilical cord blood—the blood that remains in the placenta after birth—can be collected and stored frozen for years. A well-accepted use of cord blood is as an alternative to bone marrow as a source of hematopoietic stem cells for allogeneic transplantation to siblings or to unrelated recipients; women can donate cord blood for unrelated recipients to public banks. However, private banks are now open that offer expectant parents the option to pay a fee for the chance to store cord blood for possible future use by that same child (autologous transplantation.

What next for preimplantation genetic screening? A polar body approach!

Screening of human preimplantation embryos for numerical chromosome abnormalities has been conducted mostly at the preimplantation stage using fluorescence in situ hybridization. However, it is clear that preimplantation genetic screening (PGS) as it is currently practiced does not improve live birth rates. Therefore the ESHRE PGS Task Force has decided to start a proof of principle study with the aim of determining whether biopsy of the first and second polar body followed by subsequent analysis of the complete chromosome complement of these polar bodies using an array based technique enables a timely identification of the chromosomal status of an oocyte. If the principle of this approach can be proven, it is obvious that a multicentre randomized controlled trial should then be started to determine the clinical value of this technique. In this way the ESHRE PGS Task Force hopes to redirect preimplantation screening from the blind alley to the main road of assisted reproduction

Errors in chromosome segregation during oogenesis and early embryogenesis

Errors in chromosome segregation occurring during human oogenesis and early embryogenesis are very common. Meiotic chromosome development during oogenesis is subdivided into three distinct phases. The crucial events, including meiotic chromosome pairing and recombination, take place from around 11 weeks until birth. Oogenesis is then arrested until ovulation, when the first meiotic division takes place, with the second meiotic division not completed until after fertilization. It is generally accepted that most aneuploid fetal conditions, such as trisomy 21 Down syndrome, are due to maternal chromosome segregation errors. The underlying reasons are not yet fully understood. It is also clear that superimposed on the maternal meiotic chromosome segregation errors, there are a large number of mitotic errors taking place post-zygotically during the first few cell divisions in the embryo. In this chapter, we summarise current knowledge of errors in chromosome segregation during oogenesis and early embryogenesis, with special reference to the clinical implications for successful assisted reproduction

Identification of a Novel Single Nucleotide Polymorphism of HADHA Gene at a Referred Primer-binding Site During Pre-diagnostic Tests for Preimplantation Genetic Diagnosis

The pre-diagnostic test for preimplantation genetic diagnosis (PGD) of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency was performed by polymerase chain reaction (PCR) and direct sequencing for hydroxyacyl-Coenzyme A dehydrogenase/3-ketoacyl-Coenzyme A thiolase/enoyl-Coenzyme A hydratase (HADHA) gene. We obtained unexpected genotyping results of HADHA gene by allele drop-out in the analysis of patients' genomic DNA samples with a referred PCR primer set. Upon further analysis with a re-designed primer set, we found a novel single nucleotide polymorphism (SNP) at the referred primer-binding site in the normal allele of HADHA gene (NT_022184, 5233296 a>t). We found that the frequency of this novel SNP was 0.064 in Korean population. Pre-diagnostic test using single lymphocytes and clinical PGD were successfully performed with the re-designed primer set. Nineteen embryos (95.0%) among 20 were successfully diagnosed to 5 homozygous mutated, 8 heterozygous carrier and 6 wild type. Among 6 normal embryos, well developed and selected 4 embryos were transferred into the mother's uterus, but a pregnancy was not achieved. We proposed that an unknown SNP at primer-binding sites would be a major cause of allele drop-out in the PGD for single gene disorder

Statistical data on pediatric congenital musculoskeletal anomalies (malformations) in St. Petersburg

Introduction A scientifically-based knowledge on the incidence, dynamics of detection and structure of congenital malformations of the musculoskeletal system (CMMS) has both practical and scientific significance. For many years, the Turner Institute has close scientific and practical ties with the state public health institution "Diagnostic Medical and Genetic Center" of St. Petersburg which carries out a regional monitoring of congenital disorders in St.Petersburg. Our objective was to present regional statistical data on the CMMS detection and structure in newborns and children of the first and second years of life, morbidity and disability in children aged 0-17 years in connection with congenital malformations of the musculoskeletal system, to study the proportion of CMMS patients in the orthopedic clinic and their need for surgical, including high-tech, treatment, and dispensary follow-ups in outpatient orthopaedic settings. Material and methods Regional statistics of St. Petersburg on prevalence, dynamics and structure of congenital malformations of the musculoskeletal system in children born in St. Petersburg in 2001–2015 were analyzed. The statistical data on the prevalence of congenital malformations of the musculoskeletal system in children aged 0–17 years in St. Petersburg were studied. Based on the studies conducted at the Turner Institute in 2014–2016, the proportion of patients treated for congenital malformations of the musculoskeletal system was revealed as well as their need for surgical treatment. Peculiarities of dispensary follow-ups of CMMS patients at orthopedic consultations of children's clinics of St. Petersburg were analyzed. Results and discussion The prevalence and structure of congenital malformations of the musculoskeletal system in 783,000 children born in St. Petersburg in the period of 2001–2015 are presented in accordance with blocks Q65–Q79 of ICD-10. Diagnostic results of congenital malformations of the musculoskeletal system in newborns (2.70 ‰) and in children of the same group until they reached three years of age (4.21 ‰) were studied in dynamics. Infacnts and children up to 17 years old with congenital malformations of the musculoskeletal system are under regular supervision of orthopedic surgeons. Disability due to congenital anomalies and malformations takes the third place among all the diseases detected in patients aged 0-17 years, established by pediatric medical and social expert boards of St. Petersburg. At the clinic of the Turner Institute, the proportion of patients with CMMS among all admitted patients was 38.6 %. Among them, 78 % of patients with CMMS received surgical treatment, of which 80 % of operations were performed using high technologies. Conclusions Statistics on congenital malformations of the musculoskeletal system in newborns and children under 3 years old and a high level of their disability shows the need in a specialized care for these children, including high-tech surgical treatment