Alison Lashwood

The future of prenatal diagnosis: rapid testing or full karyotype? An audit of chromosome abnormalities and pregnancy outcomes for women referred for Down's Syndrome testing

Objective  To assess the implications of a change in prenatal diagnosis policy from full karyotype analysis to rapid trisomy testing for women referred primarily for increased risk of Downs Syndrome.

Preimplantation genetic diagnosis of skin fragility–ectodermal dysplasia syndrome

Skin fragility–ectodermal dysplasia syndrome is an autosomal recessive disorder caused by loss‐of‐function mutations in the desmosomal protein, plakophilin 1. Clinically, there may be considerable morbidity from extensive skin erosions and painful fissures on the palms and soles. In the absence of any specific treatment, prenatal diagnosis is an option for couples at reproductive risk of recurrence. In 2000, we developed and applied a single cell nested polymerase chain reaction protocol to test one couple for compound heterozygous plakophilin 1 gene mutations by preimplantation genetic diagnosis (PGD). Although pregnancy was established, an unrelated trisomy 22 led to a spontaneous abortion. However, eight embryos of known genetic status were cryopreserved at that stage, and we planned to undertake subsequent frozen embryo replacement cycles that might lead to the birth of an unaffected child in this family. Embryo cryopreservation was carried out in June 2000 using standard protocols in a three‐step freezing procedure. Four embryos were thawed in March 2003, one of which was viable and was used in a frozen embryo replacement cycle, but pregnancy did not occur. The remaining four embryos were thawed in February 2004, two of which were viable (both carriers of the paternal mutation) and these were used in a second frozen embryo replacement cycle, and a singleton pregnancy was established. The childs plakophilin 1 genotype was assessed by direct nucleotide sequencing across the site of both potential mutations. Following two frozen embryo replacement cycles, and almost 4 years after the initial embryo biopsy and mutation analysis, a pregnancy was achieved that progressed to term with the birth of a healthy baby girl. Nucleotide sequencing of cord blood DNA, taken immediately after delivery, showed that the child was a heterozygous carrier of the paternal mutation but not of the maternal mutation. This case demonstrates the value of embryo cryopreservation, which can increase the number of embryo replacement procedures and hence the cumulative pregnancy rate per retrieval cycle. Moreover, this is the first report of successful full‐term pregnancy and birth of a healthy baby following exclusion of a severe genodermatosis by PGD. The successful outcome of PGD in this case illustrates what is technically possible for couples at risk of recurrence of a severe inherited skin disease.

Preimplantation genetic diagnosis for the prevention of sickle cell disease: Current trends and barriers to uptake in a London teaching hospital

Introduction. Sickle cell disease (SCD) is a clinically significant hemoglobinopathy with increasing global incidence. We describe our experience of using pre-implantation genetic diagnosis (PGD) for the prevention of SCD at a tertiary referral centre in London. Methods. Between January 2002 and December 2007, of 78 at-risk couples referred for PGD treatment, 12 couples (15%) underwent 16 PGD cycles for the prevention of SCD. Results. The live birth rate was 13% per initiated cycle, 18% per embryo transfer and 17% per couple. Conclusions. Although PGD for prevention of the birth of a child affected by SCD is a viable treatment option for couples at risk of having an affected child, potential barriers to uptake of this service need to be fully addressed to ensure its availability to all couples seeking to avoid having a child affected with SCD.

Complex Issues in PGD

The process of PGD is complex and can be challenging for both professionals and patients alike. However, there are additional complexities that arise and may not be obvious to the practitioner new to PGD. Each centre offering PGD will work within its own practical, ethical and moral framework and, where present, in accordance with specific national regulations. This chapter will address some of the issues that require further consideration when providing a PGD clinical service.

New Developments in PGD

PGD is a fast-changing landscape of reproductive medicine and constantly adopts new developments to improve its availability, accuracy and safety. These developments have been made possible because of rapid advances in assisted conception techniques and genetic testing tools. This chapter will cover some of those new developments, which are gradually being incorporated into the day-to-day PGD service.

Training and Accreditation in PGD

PGD is a complex process that requires a large team with diverse but overlapping skill sets. For PGD to be safe and competently practised, each area requires high standards of clinical and laboratory practice. In the UK and throughout the EU, accreditation and training systems have been set in place to ensure quality and suitable training.

Genetic Counselling and Its Role in PGD

Best practice recommends that counselling should be offered to all couples requesting PGD and is provided in a nondirective manner by an appropriately qualified professional. However, the process of PGD is by nature complex and requires a high level of clinical and laboratory understanding, including the practicalities of assisted reproduction treatment, some aspects of which may be unfamiliar to even experienced geneticists and general genetic counsellors. This chapter discusses some issues particular and peculiar to counselling patients considering PGD.

The future of prenatal diagnosis : Rapid testing or full karyotype? an audit of chromosome abnormalities and pregnancy outcomes for women referred for Down's syndrome testing

At present, women at increased risk of fetal Down syndrome because of advanced maternal age, an abnormal screening test result, or a previous affected child are offered genetic amniocentesis with full fetal karyotype analysis. The advent of reliable and efficient rapid molecular techniques for identifying numeric chromosome abnormalities raises the question of whether a full fetal karyotype analysis is necessary when samples are analyzed solely because the risk of Down syndrome is increased. Without complete karyotyping, there is a risk that chromosomal abnormalities not demonstrated by rapid trisomy testing will go undiagnosed. However, some of these fetuses would have a malformation evident on ultrasound scanning, and a complete karyotype analysis would be offered. At the same time, some abnormal genotypes will have no significant phenotypic sequelae visible by ultrasound, some may be inherited and not associated with phenotypic abnormalities, and others will be of uncertain significance, raising parental anxiety and possibly resulting in unnecessary pregnancy terminations. This retrospective review included 32,674 pregnant women living in or near London who had invasive prenatal diagnosis from 1996 to 2002. More than three fourths of samples (24,891) were from women referred chiefly for Down syndrome testing. Among these samples were 118 sex chromosome abnormalities and 153 autosomal abnormalities not found by rapid testing (0.62%). Fifty-five of the 118 pregnancies with fetal sex chromosome abnormalities delivered at term; in 44 the outcome was unknown and 19 miscarried or were terminated. Among the 153 pregnancies with fetal autosomal abnormalities, the prognosis was classified as good for 98, uncertain for 37, and poor for 18. The 98 cases with a good prognosis included 46 live-born infants, 3 pregnancy terminations, one case each of intrauterine death and miscarriage, and 47 whose outcome was unknown. Of 37 cases with an uncertain prognosis, 20 resulted in a live-born infant, 5 were terminations, and in 12, the outcome was not ascertained. Among 18 cases with a poor prognosis were a single live-born infant, 2 miscarriages, 11 terminations, and 4 with unknown outcomes. In a separate analysis of phenotypically abnormal children under age 5 brought in for evaluation from 1995 to 1997, there were 90 nonnumeric chromosome abnormalities of which 78 were unbalanced and 12 were balanced chromosome rearrangements. Considering that there were approximately 46,430 live births per year in the referral region over the study period, the investigators estimated that the proportion of living children with unbalanced chromosome abnormalities causing concern in the first 5 years of life was 0.06%. The risk of having an infant with a nonnumeric unbalanced chromosomal abnormality was no higher in women at increased risk of a Down syndrome pregnancy than in those lacking such risk. The investigators concluded that if prenatal karyotyping was replaced by molecular trisomy testing for women at risk of a Down syndrome birth, substantial financial savings would result, and the results would be available rapidly and would not be ambiguous. In addition, anxiety will be lessened, and possibly unneeded terminations of pregnancy would be avoided.