Preimplantation Genetic Testing

Recent Advances in Reproductive Medicine

Darren K. Griffin, Gary L. Harton, Darren K. Griffin, Gary L. Harton

• Editore: CRC Press
• Anno: 2020
• ISBN:
  9780429820304
• Edizione: 1
• Argomento: Medicine
• Categoria: Medical Theory, Practice & Reference

Preimplantation genetic testing (PGT) is now well established as a valuable treatment option for patients wishing to start or continue a family, for a range of indications from advanced maternal age to high risk of transmitting inherited disease. This text brings together contemporary thinking from international opinion leaders and will be an invaluable guide for practitioners in Reproductive Medicine wishing to keep pace with the latest developments and clinical data.

1

Preimplantation Genetic Testing and Reproductive Genetics from a Physician’s Perspective

Kateřina Veselá

Contents

Introduction

Cytogenetic Testing

Multiple-Gene NGS Panels

Description of Molecular Genetic Methods Used in the “PANDA” Panel Clinically at Repromeda, Brno, Czech Republic

Cystic Fibrosis

Spinal Muscular Atrophy

Deafness (Mutation in Connexin 26)

Fragile X Syndrome

Diagnosis of Other Potential Fertility Disorders

Genetic Testing of Gamete Donors

Therapeutic Procedures for Fertility Disorders and Genetic Defect Risks Using Genetic Methods

PGT-A

Mosaicism

Genetic Methods to Detect the Window of Implantation

Genetic Testing in the Surrogacy Program

Genetic Methods in the Control of Therapeutic Results

Summary

References

Introduction

Reproductive genetics is now inseparably linked to reproductive medicine procedures and is becoming an integral part thereof. It has been applied in the diagnosis of factors of infertility and genetic disorder carrier status. This is specifically used for screening assessments before admitting a couple to an in vitro fertilization (IVF) program for targeted diagnosis of hereditary diseases or defects, or as part of preimplantation genetic testing (PGT) procedures. In many cases it is becoming an integral part of controlling therapeutic results in the form of noninvasive or invasive prenatal diagnosis.

Reproductive-genetic counseling in infertile couples is a comprehensive communication process purposed to evaluate a risk for genetic disorder in an offspring and to discuss measures to minimize that risk and improve the results of the treatment. Options for optimal testing and screening, interpretation and implications of test results, further education about a potential genetic diagnosis and prognosis, and emotional support are highly important aspects of a reproductive-genetic counseling visit. The core ethical principles of genetic counseling are the autonomy of the individual or couple, their right to full information, and the highest standards of confidentiality.

Although crude monetary arguments are not generally used to justify the provision of genetic counseling services, financial analysis might show a net cost savings to society/family by the reduction of expenditure on caring for those with serious genetic disease or disability.

Our contemporary professional goals in reproductive genetics are quite different from former ideas of eugenic medicine (“the health of the people,” i.e., of the race). Respect for individual autonomy takes precedence over measures of the impact of genetic services on the population. We have always to comply with the wish for having a healthy baby, which is universal in all couples. Reproductive genetics is a part of medicine whose general purpose is to prevent or at least minimize suffering and distress.

Cytogenetic Testing

Basic cytogenetic tests used in reproductive medicine include karyotyping, performed for many years using G-banding [1] in cultured peripheral blood cells (lymphocytes). One of the best-established means of genetic diagnosis, adaptations of the original approach are used to this day, supplemented by enhanced banding techniques and digitized analysis. Given the dynamic development of molecular biology, this method has, in part, been successfully converted to a molecular genetic platform for routine use in a short time horizon. Currently, flatbed microarrays and the single nucleotide polymorphism (SNP) array method [2] are used for closer specifications of the findings of classical karyotyping if there are any unclear aspects, and in special indications. Microarrays provide considerably higher resolving power compared to G-banding, and can be used to detect microdeletions or microduplications as low as 0.5 Mb.

Expanded carrier screening (ECS) of patients as well as gamete donation is performed ever more commonly as part of testing before inclusion in the IVF program. Similarly, as in the case of new preimplantation and prenatal testing methods, the development of ECS has been made possible by the arrival of newer developments in molecular genetics [3].

Multiple-Gene NGS Panels

The introduction of next-generation sequencing (NGS) (including massive parallel sequencing [MPS]) has allowed a substantially wider and more detailed analysis of the genetic causes and relationships of pathological conditions [4]. Multiple-gene panels allow testing of many genes in a very short time. Such panels are typically a set of genes tested in parallel; physically, it is a set of DNA segments used to prepare a library, subsequently used as the basis for sequencing [5,6].

Tests using multiple-gene panels are most commonly used in oncology to detect inherited mutations in oncogenes [7], and in cardiological diagnosis [8]. Currently, their use is rapidly increasing for use in reproductive medicine [4–6]. Some reproductive clinics use standardized commercial panels, while others design an individual structure and assign the production of panels created based on their own specific requirements.

The purpose of using panels in modern reproductive medicine is to determine any potential genetic causes of fertility disorders in the man and woman, to uncover any gene mutations that might lead to the development of serious inherited diseases in the offspring, and finally to detect any factors posing potential risks to infertility therapy which could have potentially adverse impacts on the result.

Regularly tested gene mutations that cause the most common serious inherited diseases include mutations in the CFTR gene causing cystic fibrosis, the SMN1 gene causing spinal muscular atrophy, the GJB2 gene causing nonsyndromic deafness, and the FMR1 gene causing fragile X syndrome. Sites in different countries may include isolated tests of various mutations or implement these in multiple-gene panels with respect to habitual practice, patient requirements, legal regulations, or guidelines of a local professional association.

Description of Molecular Genetic Methods Used in the “PANDA” Panel Clinically at Repromeda, Brno, Czech Republic

The scientists and clinicians at Repromeda have developed a custom NGS panel that assesses a number of specific mutations as noted previously. Details of this test, called PANDA, are included next to highlight one specific use of custom panels used during an IVF cycle.

In brief, the test includes steps for performing preparation of the library: Custom Amplicon Library NEXTFlex NOVA-4301-03 Bioo Scientific Corp. (Perkin Elmer), sequencing using the MiSeq system (Illumina), evaluation using SeqPilot software (JSI Medical Systems), Repromeda bioinformatics software—SOP00417.

Additional detection test (CGG)n—Fragile X, Repromeda CGG RP PCR detection and AmplideX FMR1 PCR Kit (Asuragen), fragmentation analysis—SOP 00415. This is a diagnostic genetic test designed for the testing of mutations that cause the most common genetic diseases in the Central European population; furthermore, thrombophilic mutations and genes/variants clinically related to inferti...