Molecular strategies for pre-implantation genetic diagnosis of single gene and chromosomal disorders

Preimplantation Genetic Diagnosis of Multiple Endocrine Neoplasia Type 2A Using Informative Markers Identified by Targeted Sequencing

BACKGROUND

The revised guidelines for the management of medullary thyroid carcinoma recommend that genetic counseling regarding reproductive options, including preimplantation genetic diagnosis (PGD), be considered for all RET mutation carriers of reproductive age to avoid the transmission of multiple endocrine neoplasia type 2 (MEN2). However, the high complexity and cost of PGD have hindered its widespread use. Thus, it is necessary to establish a simple and relatively inexpensive method to facilitate the PGD of MEN2.

PATIENTS AND METHODS

A customized Nimblegen EZ sequence capture array was designed to capture the targeted regions, including the RET gene, and 1 Mb range on each side of the RET gene. Targeted, capture-based next-generation sequencing of three members of one family with MEN2A (the couple and the paternal father) was conducted to identify the informative markers. The diagnosis of the embryos was achieved through haplotype analysis based on informative markers and causative mutation.

RESULTS

Based on the sequencing results, 173 informative markers were detected, which were sufficient for the subsequent use for PGD. Seven informative markers and the causative mutation (RET^C634Y) were selected and subjected to Sanger sequencing. Through haplotype analysis, four embryos without inheritance of the mutation haplotype of the RET gene were diagnosed as unaffected. One unaffected embryo was transferred, with one healthy baby born at 38 gestational weeks.

CONCLUSIONS

Targeted, capture-based next-generation sequencing for identification of informative markers together with Sanger sequencing is an easy and efficient method for the PGD of monogenic diseases such as MEN2.

Genetic and epigenetic risks of assisted reproduction

Assisted reproductive technology (ART) is used primarily for infertility treatments to achieve pregnancy and involves procedures such as in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), and cryopreservation. Moreover, preimplantation genetic diagnosis (PGD) of ART is used in couples for genetic reasons. In ART treatments, gametes and zygotes are exposed to a series of non-physiological processes and culture media. Although the majority of children born with this treatment are healthy, some concerns remain regarding the safety of this technology. Animal studies and follow-up studies of ART-borne children suggested that ART was associated with an increased incidence of genetic, physical, or developmental abnormalities, although there are also observations that contradict these findings. As IVF, ICSI, frozen-thawed embryo transfer, and PGD manipulate gametes and embryo at a time that is important for reprogramming, they may affect epigenetic stability, leading to gamete/embryo origins of adult diseases. In fact, ART offspring have been reported to have an increased risk of gamete/embryo origins of adult diseases, such as early-onset diabetes, cardiovascular disease, and so on. In this review, we will discuss evidence related to genetic, especially epigenetic, risks of assisted reproduction.

Reproductive outcome following pre-implantation genetic diagnosis (PGD) in the UK

In 2013, the National Health Service Commissioning board centralized the funding in England for up to three cycles of pre-implantation genetic diagnosis (PGD) for couples who have, or are carriers of, a specific genetic disorder. This study presents the historical data of PGD cycles and their clinical outcomes in UK as extrapolated from the national data registry. Retrospective analysis of outcome of cycles undergoing pre-implantation genetic diagnosis in the UK over the past 20 years was performed from the Human Fertilisation and Embryology Authority database (n = 2974). Binary logistic regression was used to determine trends over time and adjusted for maternal age. Briefly, the number of PGD cycles has risen 127-fold from 1991 to 2012 with 3.6-fold increase (360% rise) from 2004 to 2012. A total of one in four embryos following pre-implantation genetic diagnosis did not reach embryo transfer and 92% of these were due to a failure to survive. The live birth rate has risen over 20 years and there has been a steady decline in reported incidence of congenital abnormalities (p < 0.07). PGD has thus emerged as a safe and effective alternative to prenatal diagnosis but with ever evolving technological advances, a robust system of data collection that incorporates techniques used and reporting of mutation-specific clinical outcomes is suggested.

Robust and tissue-independent gender-specific transcript biomarkers

CONTEXT

Correct gender assignment in humans at the molecular level is crucial in many scientific disciplines and applied areas.

MATERIALS AND METHODS

Candidate gender markers were identified through supervised statistical analysis of genome wide microarray expression data from human blood samples (N = 123, 58 female, 65 male) as a training set. The potential of the markers to predict undisclosed tissue donor gender was tested on microarray data from 13 healthy and 11 cancerous human tissue collections (internal) and external datasets from samples of varying tissue origin. The abundance of some genes in the marker panel was quantified by RT-PCR as alternative analytical technology.

RESULTS

We identified and qualified predictive, gender-specific transcript markers based on a set of five genes (RPS4Y1, EIF1AY, DDX3Y, KDM5D and XIST).

CONCLUSION

Gene expression marker panels can be used as a robust tissue- and platform-independent predictive approach for gender determination.