SEETHRAM Prenatal Screening
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27/07/2017 Prenatal Screening All that you need to know….. Fertility Symposium Ken Seethram, MD, FRCSC, FACOG Pacific Centre for Reproductive Medicine Clinical Assistant Professor, UBC & University of Alberta [email protected] Outline • To understand • Prenatal Screening and amniocentesis/CVS • Non-Invasive Prenatal Testing/Screening • To understand the scope of NIPT and its variations • To understand the detection rates and limitations of NIPT • To understand the various forms of prenatal screening, and who gets what in BC 1 27/07/2017 Disclosure • I have no financial interest in the current NIPT providers – we receive no research grants, educational grants, or other initiatives from any NIPT provider • We draw and send plasma on patients for NIPT in our centre • We perform first trimester screening (non-insured service) in our centre • Warning: trade names will be used during this talk Prenatal Screening & Diagnosis for Chromosome Abnormalities • T21 is one of the most common aneuploidy to affect live-born children and has a background prevalence of 1:691, increasing with maternal age • What causes T21 – hypo-methylation by the extra chromosome • Prenatal diagnosis relies upon the procurement of fetal cells via amniocentesis (ACT) / trophoblast via chorionic villus sampling (CVS) 2 27/07/2017 1977-That would have been the end of this talk Prenatal Screening & Diagnosis for Chromosome Abnormalities • Simpler times back then; if your age based risk exceeded the risk of diagnostic testing, then do the test (which was roughly age 35-38) • So the only screening tool we had was age • What is the risk of Amniocentesis or CVS? • For the last 40 years, it has been quoted at 1% 3 27/07/2017 What is the RISK of CVS/ACT • A recent meta-analysis (Akolekar, et al (2015) Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis. Ultrasound in Obstetrics and Gynecology 45(1):16): • 42,000 women who underwent ACT and 138,000 who did not, data collected >1999 • Attributable miscarriage risk: 0.11% • 54,000 women who underwent CVS and 670,000 who did not, data collected >1999 • Attributable miscarriage risk: 0.22% • Odibo, et al (2008) Revisiting the fetal loss rate after second-trimester genetic amniocentesis: a single center's 16-year experience. Obstetrics and Gynecology 11(3):589 • 11 746 amniocenteses and 5243 CVS • 0.13% loss rate in amnio and 0.7% loss rate in CVS was no different than the loss rate in those without invasive procedures • Our previously agreed-upon 1% may not be so true Invasive Testing • The risks of invasive testing should govern the decision to do the test. • However….end of the day – nobody wants invasive testing even if the risk of loss is 1/1000 4 27/07/2017 What is the point of prenatal screening? • To reduce the risk of invasive testing • by limiting the invasive test to those most in need (the highest risk people) Prenatal screening • And How? • Age • Double screening>Triple marker screening> Quad Screening • MSAFP for Neural tube defect screening in the early 80’s was then linked with hCG for T21 detection • 1991 (Cuckle and Wald) published in the BJOB – uE3, hCG for T21 detection • Combined this became triple marker screening • Modified in 1996 by the addition of dimeric Inhibin-A to become QUAD screen 5 27/07/2017 Prenatal screening • And How? • Age • Double screening>Triple marker screening>Quad Screening • First Trimester Combined Screening (NT+NB+DV+PAPP-A+bHCG) • BMJ 1992 – K. Nicolaides published on the use of beta-hCG, PAPP-A and a single ultrasound measurement at 12w called nuchal translucency (NT) • Modified since 1992 to include nasal bone, FHR, ductus venosus flow (hepatic vein flow) using color flow Doppler measurements • Accreditation provided through single site – Fetal Medicine Foundation, UK • Detection rate: 96% with screen positive rate = 3% Prenatal screening • And How? • Age • Double screening>Triple marker screening>Quad Screening • First Trimester Combined Screening (NT+NB+DV+PAPP-A+bHCG) 6 27/07/2017 Prenatal screening • By the end of 2009, there were really two camps in prenatal screening Prenatal screening Second Trimester 100 First Trimester People People •Serum based •Ultrasound based Pleasers •Placental screening (QUAD) •Early •PAPP-A + Quad (SIPS) •Dates •NT + PAPP-A + QUAD •Twins etc (IPS) •Anomaly screening DR 88% DR 96% SRP 3% DR 75% SRP 3% SRP 5% 7 27/07/2017 Prenatal screening • And How? • Age • Double screening>Triple marker screening>Quad Screening • Combined First Trimester Screening • And then things got really complicated in 2011…..NIPT NIPT – ability to detect ‘fetal’ DNA • Emerged in 2011, but first described in 1997 • “cell-free ‘fetal’ DNA (cffDNA),” actually derived from the placenta=4% of all free-DNA in the maternal blood • Can be detected as early as 4-5 weeks of gestation • Usually does not exceed 150 base pairs of length (very small fragments) but the entire fetal genome is represented • Keep in mind: • Our entire genome - 6.5B base pairs • Chromosome 1 has 249M base pairs • Chromosome 21 has 48M base pairs • Chromosome 22 has 49.5M base pairs • So there’s a lot of analysis required to re-construct part or all of the fetal genome from these bits of DNA 8 27/07/2017 Human Genome Project in the meantime… Human Genome Project and NIPT • Fragments of DNA can then be compared against library’s like Venter’s Human Genome Library (HuRef) to essentially either sequence the genome from those fragments, or use targeted gene analysis to count signals 9 27/07/2017 NIPT • How does it work? • In aneuploidy, the placenta is also aneuploid, therein releasing more DNA of particular chromosomes versus the balanced number expected – this principle is the basis for NIPT • Blood draw – timing depends on the product, but generally as early as 9w. Methods – NIPT (1997-2015) • 1997 First paper published demonstrating the presence of cell free fetal DNA. (PCR) • 2008 Use of s-MPS to identify millions of fragments of DNA and their specific chromosome origin. This is whole genome sequencing (MaterniT21) • Very costly, and timely, requiring up to 10M base pairs to be sequenced • 2009-2010 – introduction of targeted sequencing for identification of set loci • on certain chromosomes (Harmony) • 2012 -SNP array (Panorama) – generating a virtual karyotype by determining the copy number of each SNP on the array and aligning the SNP’s in chromosomal order 10 27/07/2017 Types of NIPT S-MPS Whole Genome ex. MaterniT21 NIPT Panorama SNP Array Targeted Harmony NIPT • To clarify some misnomers: • It’s not non-invasive (although, akin to every other mode of screening, the fetal risk is zero) • It’s not testing or diagnosis (although up to 7% of women will proceed with termination after a positive NIPT without diagnostic confirmation) • It’s not cell free fetal DNA – it’s placental DNA • It’s not pronounced NIP-TEE 11 27/07/2017 NIPT • How accurate is it? • For T21 - >99.2% with 0.1% screen positive rate • What is the biggest error? • Non Reporting • of all the published studies, the rate ranges from 1%-10% and 32% of the time, when you read a second sample, you’ll still not get enough fetal fraction to provide analysis • On average, 3-4% of samples are non reported Targeted Sequencing (Harmony) • 99.9% specificity with 0.103% FPR • Looking for specific genes with 13/18/21 loci and counting their DNA load relative to genes from other chromosomes • Not as great for T13 and T18 (about 90%), but for T21 it’s excellent • <4.0% = low fetal fraction – non reporting risk • But it’s less expensive than MPS, and excellent for T21 12 27/07/2017 NIPT using SNP array (Panorama) • Can provide information about the parent of origin of aneuploidy, recombination and inheritance of mutations • Can provide information on a subset of other chromosomal rearrangements such as Angelman syndrome, Prader-Willi, DiGeorge syndrome • Can use lower fetal fraction (2.8%) – therefore theoretically less non- reporting • May flag triploidy or vanishing twins NIPT using whole genome • Massively parallel sequencing based (BGI, Beijing Genomics Institute) H. Zhang, 2015 • 147,314 samples • Sensitivities: • T21 99.17% • T18 98.24% • T13 100% • Human Genome project – 1988-2003 = 2.7B 13 27/07/2017 What NIPT is commercially available? • Ariosa (Roche) Harmony • Verinata Verifi • Sequenom MaterniT21 Plus • NIPT plus • 22q deletion syndrome ( DiGeorge ) • 5p ( Cri-du-chat syndrome ) • 15q ( Prader-Willi/Angelman syndromes ) • 1p36 deletion syndrome • 4p ( Wolf-Hirschhorn syndrome ) • 8q ( Langer-Giedion syndrome ) • 11q ( Jacobsen syndrome ) • Trisomy 16 • Trisomy 22 • NIPT alone VisibiliT • Genome Wide Maternit GENOME • Labcorp – Integrated Genetics Informaseq • Natera – NIPT plus microdeletions Panorama • BGI NIFTY • Berry Genomics BambiniTest • Premaitha IONA test • NIPD Genetics Veracity Which NIPT is best? • The best test is the one which is accurate, cost effective, and broad in perspective • Frankly all of them are superb in detection rates • But…here’s the problem……NIPT is being sold as prenatal screening – it’s not 14 27/07/2017 NIPT IS NOT Prenatal Screening • NIPT = Down syndrome screening. • NIPT is another part of • While we can screen with NIPT less well for T18, T13, 45X, and a smattering of the prenatal screen rare disorders, NIPT is T21 screening • There are some ethical drawbacks to this: • It’s also not cytogenetics • We might ‘normalize’ testing and termination so should never replace • We might invest less in support for