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

Human embryonic stem cells from aneuploid blastocysts identified by pre-implantation genetic screening

Human embryonic stem cells are derived from the inner cell mass of pre-implantation embryos. The cells have unlimited proliferation potential and capacity to differentiate into the cells of the three germ layers. Human embryonic stem cells are used to study human embryogenesis and disease modeling and may in the future serve as cells for cell therapy and drug screening. Human embryonic stem cells are usually isolated from surplus normal frozen embryos and were suggested to be isolated from diseased embryos detected by pre-implantation genetic diagnosis. Here we report the isolation of 12 human embryonic stem cell lines and their thorough characterization. The lines were derived from embryos detected to have aneuploidy by pre-implantation genetic screening. Karyotype analysis of these cell lines showed that they are euploid, having 46 chromosomes. Our interpretation is that the euploid cells originated from mosaic embryos, and in vitro selection favored the euploid cells. The undifferentiated cells exhibited long-term proliferation and expressed markers typical for embryonic stem cells such as OCT4, NANOG, and TRA-1-60. The cells manifested pluripotent differentiation both in vivo and in vitro. To further characterize the different lines, we have analyzed their ethnic origin and the family relatedness among them. The above results led us to conclude that the aneuploid mosaic embryos that are destined to be discarded can serve as source for normal euploid human embryonic stem cell lines. These lines represent various ethnic groups; more lines are needed to represent all populations

Savior siblings and Fanconi anemia : analysis of success rates from the family's perspective

Purpose:The current curative treatment of Fanconi anemia is hematopoietic stem cell transplantation; this treatment has a higher rate of successful outcome when donors are compatible siblings. Therefore some families opt to have a healthy and compatible baby after selecting an embryo using preimplantation genetic diagnosis with human leukocyte antigen (HLA) typing. This study aims to estimate the success rate of this procedure from the family's perspective.Methods:Genetic and embryology data were collected from genetic reports provided by the families.Results:A total of 524 oocytes (14.1 oocytes/cycle) and 299 embryos were generated (8.0 embryos/cycle) after 38 in vitro fertilization cycles. Sixteen embryos were transferred to the uterus because they were non-Fanconi anemia and HLA matched. One baby was born. A younger couple delivered a healthy and HLA-compatible baby after four cycles. Therefore, the success rate per cycle is less than 5% (two babies from 42 trials).Conclusion:While Fanconi anemia per se does not worsen the probability of success, a critical factor is advanced maternal age; a late diagnosis leads to few transferrable embryos and high rates of aneuploidy. Families should be informed in advance of the many trials that they will probably need to undergo even if a haploidentical younger relative is available as an oocyte donor

The clinical utility of molecular diagnostic testing for primary immune deficiency disorders: a case based review

Primary immune deficiency disorders (PIDs) are a group of diseases associated with a genetic predisposition to recurrent infections, malignancy, autoimmunity and allergy. The molecular basis of many of these disorders has been identified in the last two decades. Most are inherited as single gene defects. Identifying the underlying genetic defect plays a critical role in patient management including diagnosis, family studies, prognostic information, prenatal diagnosis and is useful in defining new diseases. In this review we outline the clinical utility of molecular testing for these disorders using clinical cases referred to Auckland Hospital. It is written from the perspective of a laboratory offering a wide range of tests for a small developed country

Chromosomal Preimplantation Genetic Diagnosis: 25 Years and Counting.

Preimplantation genetic diagnosis (PGD), first successfully carried out in humans in the early 1990s, initially involved the PCR sexing of embryos by Y- (and later also X-) chromosome specific detection. Because of the problems relating to misdiagnosis and contamination of this technology however the PCR based test was superseded by a FISH-based approach involving X and Y specific probes. Sexing by FISH heralded translocation screening, which was shortly followed by preimplantation genetic screening (PGS) for Aneuploidy. Aneuploidy is widely accepted to be the leading cause of implantation failure in assisted reproductive technology (ART) and a major contributor to miscarriage, especially in women of advanced maternal age. PGS (AKA PGD for aneuploidy PGD-A) has had a chequered history, with conflicting lines of evidence for and against its use. The current practice of trophectoderm biopsy followed by array CGH or next generation sequencing is gaining in popularity however as evidence for its efficacy grows. PGS has the potential to identify viable embryos that can be transferred thereby reducing the chances of traumatic failed IVF cycles, miscarriage or congenital abnormalities and facilitating the quickest time to live birth of chromosomally normal offspring. In parallel to chromosomal diagnoses, technology for PGD has allowed for improvements in accuracy and efficiency of the genetic screening of embryos for monogenic disorders. The number of genetic conditions available for screening has increased since the early days of PGD, with the human fertilization and embryology authority currently licensing 419 conditions in the UK [1]. A novel technique known as karyomapping that involves SNP chip screening and tracing inherited chromosomal haploblocks is now licensed for the PGD detection of monogenic disorders. Its potential for the universal detection of chromosomal and monogenic disorders simultaneously however, has yet to be realized