Maternal blood contamination of collected cord blood can be identified using DNA methylation at three CpGs
Morin et al. Clinical Epigenetics
Maternal blood contamination of collected cord blood can be identified using DNA methylation at three CpGs
Alexander M. Morin 0 3
Evan Gatev 0 3
Lisa M. McEwen 0 3
Julia L. MacIsaac 0 3
David T. S. Lin 0 3
Nastassja Koen 2
Darina Czamara 1
Katri Räikkönen 7
Heather J. Zar 6
Karestan Koenen 5
Dan J. Stein 2
Michael S. Kobor 0 3 4
Meaghan J. Jones 0 3
0 Centre for Molecular Medicine and Therapeutics, BC Children's Hospital, Department of Medical Genetics, University of British Columbia , 950 W 28th Ave, Vancouver, BC V5Z 4H4 , Canada
1 Max Planck Institute of Psychiatry, Department of Translational Research in Psychiatry , Kraepelinstraße 2-10, 80804 Munich , Germany
2 Department of Psychiatry and Mental Health, South African Medical Research Council (SAMRC) Unit on Anxiety and Stress Disorders, University of Cape Town, Groote Schuur Hospital , J2, Anzio Road, Observatory, Cape Town , South Africa
3 Centre for Molecular Medicine and Therapeutics, BC Children's Hospital, Department of Medical Genetics, University of British Columbia , 950 W 28th Ave, Vancouver, BC V5Z 4H4 , Canada
4 Human Early Learning Partnership, University of British Columbia , 2208 East Mall, Vancouver, BC 02115 , Canada
5 Department of Epidemiology, Harvard T. H. Chan School of Public Health , 677 Huntington Avenue, Kresge Building, 505, Boston, MA 02115 , USA
6 Department of Paediatrics, MRC Unit on Child and Adolescent Health, University of Cape Town , Room 513 ICH Building Red Cross Children's Hospital Klipfontein Road, Cape Town , South Africa
7 Department of Psychology and Logopedics, Faculty of Medicine, University of Helsinki , P.O.Box 63, 00014 Helsinki , Finland
Background: Cord blood is a commonly used tissue in environmental, genetic, and epigenetic population studies due to its ready availability and potential to inform on a sensitive period of human development. However, the introduction of maternal blood during labor or cross-contamination during sample collection may complicate downstream analyses. After discovering maternal contamination of cord blood in a cohort study of 150 neonates using Illumina 450K DNA methylation (DNAm) data, we used a combination of linear regression and random forest machine learning to create a DNAm-based screening method. We identified a panel of DNAm sites that could discriminate between contaminated and non-contaminated samples, then designed pyrosequencing assays to pre-screen DNA prior to being assayed on an array. Results: Maternal contamination of cord blood was initially identified by unusual X chromosome DNA methylation patterns in 17 males. We utilized our DNAm panel to detect contaminated male samples and a proportional amount of female samples in the same cohort. We validated our DNAm screening method on an additional 189 sample cohort using both pyrosequencing and DNAm arrays, as well as 9 publically available cord blood 450K data sets. The rate of contamination varied from 0 to 10% within these studies, likely related to collection specific methods. Conclusions: Maternal blood can contaminate cord blood during sample collection at appreciable levels across multiple studies. We have identified a panel of markers that can be used to identify this contamination, either post hoc after DNAm arrays have been completed, or in advance using a targeted technique like pyrosequencing.
Cord blood; Contamination; DNA methylation; 450K; Genotyping; Maternal blood; Blood banking
Background
Neonatal blood from the umbilical cord at the time of
delivery is increasingly being collected for both research and
medical purposes. In research, interest in the
developmental origins of health and disease has made cord blood a
popular choice for genetic, epigenetic, and environmental
studies [
1
]. Cord blood has several physiological
differences from adult blood, such as the presence of nucleated
red blood cells and fetal hemoglobin, and is an excellent
window into the in utero environment, free of
confounding post-natal exposures [
2, 3
]. Medically, cord blood is
banked for transplantation as a source of progenitor cells
for replenishing the hematopoietic system [4]. Cord blood
can be collected after caesarian or vaginal delivery, either
preceding or following delivery of the placenta. Both
processes typically involve venipuncture of the umbilical
artery and collection into a blood bag by gravity [
4
].
Problems can arise when the collected cord blood
becomes contaminated with other cells, most frequently
maternal white blood cells [
5, 6
]. In some cases, maternal
blood cells may enter fetal circulation through the placenta.
Previous studies have shown that such contamination can
occur relatively frequently, estimated at 2–20% of collected
samples, but it makes up a very small fraction of fetal blood,
with ~10−4 to 10−5 fetal nucleated cells estimated as
maternal [
7–10
]. This small amount of contamination should
have negligible effects on the assessment (...truncated)