2023 ACMG Annual Clinical Genetics Meeting Digital Edition: Poster Gallery-Concordance Analysis of Monozygotic Twin Gestations with SNP Technology Identifies Discrepant Chromosome Findings

Pdf Summary

The study analyzed product of conception (POC) and non-invasive prenatal testing (NIPT) samples from monozygotic (MZ) twins to identify any discrepancies in chromosome findings. In the fresh POC samples, 71.4% were dizygotic (DZ) twins, 20.5% were MZ twins, and 8.1% had unknown zygosity. Of the 470 MZ twins, 7.9% had discordant chromosome findings. A SNP concordance analysis confirmed that MZ twins were identical on all chromosomes except for the discrepant chromosome finding(s). In cases with discordant NIPT results, amniocentesis and POC testing confirmed the MZ twins to be genetically concordant. These findings suggest that discrepancies in chromosome findings can occur in both POC and NIPT samples from MZ twins, potentially due to mosaicism within one or both fetuses or early postzygotic nondisjunction in one of the twins. Testing only one twin during pregnancy may miss important copy number changes (CNVs) affecting only one fetus. Further studies are needed to examine the overall rate and implications of mosaicism in MZ twins. The study emphasizes the importance of additional prenatal testing and postnatal studies in MZ twins with discordant ultrasound findings. It is also suggested that parental balanced translocations may carry a recurrence risk for CNVs affecting one fetus.

Asset Subtitle

Presenting Author - Melissa K. Maisenbacher, MS, CGC; Co-Author - Georgina Goldring, MS, CGC; Co-Author - Katherine L. Howard, LGC, CGC, MSGC; Co-Author - Russell Jelsema, MD, FACOG; Co-Author - India Bradley, MS, CGC; Co-Author - Karine Hovanes, PhD, FACMG; Co-Author - Wenbo Xu, MD, PhD, FACMG; Co-Author - Katrina Merrion, MS; Submitter Only - J. Bryce Ortiz, PhD;

Meta Tag

Cell free DNA/cfDNA

Chromosomal Abnormalities

Fetal Pathology

Noninvasive prenatal screening (NIPS)

Prenatal Diagnosis

Uniparental Disomy

Co-Author Georgina Goldring, MS, CGC

Co-Author Katherine L. Howard, LGC, CGC, MSGC

Co-Author Russell Jelsema, MD, FACOG

Co-Author India Bradley, MS, CGC

Co-Author Karine Hovanes, PhD, FACMG

Co-Author Wenbo Xu, MD, PhD, FACMG

Co-Author Katrina Merrion, MS

Presenting Author Melissa K. Maisenbacher, MS, CGC

Submitter Only J. Bryce Ortiz, PhD

Keywords

product of conception

non-invasive prenatal testing

monozygotic twins

chromosome findings

dizygotic twins

SNP concordance analysis

discordant chromosome findings

NIPT results

mosaicism in MZ twins

copy number changes