PGD: Preimplantation Genetic Diagnosis

Transcription

1 Testing on Embryo PGD, PND Mohammad Keramatipour MD, PhD Testing on Embryos Pre-implantation Genetic Diagnosis (PGD) Early embryo Pre-natal Diagnosis (PND) First trimester Second trimester 1 2 Couples with Genetic Disorders The problem: Couples with genetic disorders Affected children or family member Fertility problems Recurrent abortion, ART failure,.. Options: No other children Adoption Using donated gamete or embryo Prenatal diagnosis + possible termination Preimplantation genetic diagnosis (PGD) 3 PGD PGD: Preimplantation Genetic Diagnosis Genetic analysis of single cells to screen embryos obtained by assisted reproductive technologies prior to transfer Goal: Avoid transferring of embryos affected with a specific genetic disease PGD Historical Facts History: 1990: Human embryo biopsy at 8-cell stage is safe (Hardy et al.) 1990: Embryo sexing (X-linked disorders, Handyside et al.) 1992: Cystic fibrosis, first live born girl 1995: Duchenne muscular dystrophy: resulted in successful non-carrier female pregnancy A recent report by ESHRE: 25 centers across Europe, USA, and Australia 1561 cycles, 451 pregnancies, 251 deliveries (156 singletons, 54 twins, and 5 triplets), 279 babies born 4 4 cycles with incorrect diagnosis, one fetus with chromosomal problem 5 PGD Outcome ESHRE reports: Success rates: 22% per embryo transfer (by ESHRE) Follow up of 279 babies born: Data available for only 180 out of 279 babies Perinatal mortality rate: 3/180 Prematurity: the most common neonatal complication (67/180) Congenital malformation rate: 6.6% (3.9% major, 2.7% minor)

2 Overview of the Technology - PGD PGD stages: PGD - Technology In vitro fertilization / ICSI Ovarian hyperstimulation Egg retrieval Embryo biopsy Polar body: maternal information only Cleavage stage (8-cell stage): most common and acceptable Blastocyst Embryo screening Single cell diagnosis Cytogentic analysis Molecular analysis 7 Embryo transfer 8 PGD Day 0 Preparation of oocyte and sperm ICSI is the choice methods to avoid contamination of dead sperm inside zona Zygote (8-14 hrs) Polar body biopsy Maternal information PGD Day PGD, 3-6 Days Cleavage stage (72 hrs) Biopsy of blastomeres usually at 8-cell stage (one or two) Blastocyst (5/6 days) Trophectoderm biopsy Indications: Molecular Analysis Single gene disorders Basically any diseases: CF, DMD, Hemophilia and.. Embryo sexing Analysis of ZFY and/or ZFX genes Methodology: Single cell PCR + other molecular techniques (RFLP) Nested or hemi-nested PCR PEP (Primer Extension Pre-amplification) Whole-genome amplification of single cell genome 11

3 Locus specific PCR Choice of Methods Detection of point mutation, deletion or insertions Detecting of one mutation only The inheritance pattern of the disease?? Genetic status of the parents?? PEP following by other molecular analysis The need for screening more than one mutation Detecting the absence of an exon or part of a gene Fate of PCR product: Molecular Analysis Restriction digestion (RFLP) Heteroduplex analysis Sequencing Indirect testing (linkage analysis) Single Cell Diagnosis FISH Analysis Chromosome analysis (Fluorescent in situ hybridization, FISH) Sexing embryos X-linked disorders Chromosome abnormalities Translocation, rearrangement Age related aneuoploidy Chromosome involved: 13, 16, 18, 21, X and Y Main indications: Recurrent IVF failure Recurrent miscarriage i Embryo sexing Chromosome X Normal Female Chromosome Y Chromosome 16 Normal Male Fluorescent In Situ Hybridization Fluorescent in situ hybridization (FISH): showing interphase nuclei with trisomy 21, using chromosome 21 centromeric probe Detection of trisomies Diagnosis of Prader-Willi FISH Analysis 17 18

4 Benefits/Limitation of PGD Benefits: Accurate, sensitive, fast Avoid pregnancy termination (legal, moral, or religious abjections) Limitations: Inevitable IVF/ ICSI Ovarian hyperstimulation syndrome Birth defects rate of around 9% (4.2% in normal population) Imprinting defects (Beckwith-Wiedemann Syndrome) Bypassing natural selection Legal and ethical issues Fate of spare embryos 19 Limitations of PGD, All embryos may be affected Low success rate Cost and funding Misdiagnosis Contamination Mosaicism Allele drop-out out (ADO) Technology is complex and demanding Other Indications for PGD HLA matching Bone marrow transplantation Pre-implantation genetic screening (PGS): couples with repeated ART failure Predictive screening / testing Cancer predisposition Late onset disorders Alzheimer s Prenatal Diagnosis Definition: simply diagnosis before birth 1966, Steele and Berg, karyotyping of amniocytes Diagnosis of Down syndrome Today: Screening and diagnosis for many disorders Congenital anomalies Genetic disorders Goals of PND Genetic Counseling for PND Providing a range of informed choices to couples Provide reassurance and reduce anxiety Allow high-risk couples to have children Allow appropriate management of the pregnancy/ delivery/ and postnatal care Enable prenatal treatment of the affected fetus PND genetic counseling deals with: Risk assessment that the fetus will be affected Nature and probable consequences of the problem Risks and limitations of PND procedures Time management for the PND Advice regarding the possible need to repeat the procedure or error in diagnosis 23 24

5 Main Indication for PND Eligibility criteria: risk for the fetal abnormality should be higher than the risk of miscarriage from the procedures Indications: Advanced maternal age Previous child with a de novo chromosome abnormality Structural chromosome abnormalities in parents Family history of genetic disorders that may be diagnosed by DNA or biochemical tests Risk of neural tube defects High-risk pregnancies characterized by other screening methods Methods of PND Noninvasive testing Maternal serum alph-fetoprotein Maternal serum screen Ultrasonography Isolation of fetal cells from maternal circulation Invasive testing Amniocentesis Chorionic villus sampling (CVS) Cordocentesis Amniocentesis Removing around 15 ml of amniotic fluid Performed between weeks Risk of miscarriage: % Early amniocentesis: 2.6% miscarriage, 1.3% club foot Results: takes 2-4 weeks Diagnostic Use Chromosome analysis Culture of amniocytes Karyotyping FISH Molecular analysis DNA extraction from cultured amniocytes PCR based methods Hybridization based methods Biochemical analysis AFP level Enzymes level Corionic Villi Sampling CVS is the biopsy of tissue form the villous area of the chorion Performed between weeks Can be done transcervically or transabdominally Risk of miscarriage: 1% Advantages/Risk of CVS Advantages: CVS gives earlier result Choice method for molecular diagnosis Possible chromosomal and molecular analysis of many disorders Risks: Limitation on some biochemical analysis (AFP,.) Higher risk of miscarriage Ambiguous results (2%): follow up by amniocentesis 29 30

6 Cordocentesis PND DNA Analysis Obtaining fetal blood sample from umbilical cord Performed at week Fetal loss: 2-3% Possible chromosome/ molecular/ and biochemical analysis Fetal blood cells usually needs to be cultured for few days It is not the standard test performed here in Iran PND - Biochemical Analysis Down Syndrome Karyotyping FISH Trisomy 18 Final Remarks Our situation ti in Iran Advantage of PND is to the immediate family not tt to the population Bypassing natural selection??? 35 36

7 Thank You For Your Attention!!! 37