Project description:(1) In clinical practice and biomedical research populations are often divided categorically into distinct racial and ethnic groups. In reality, these categories comprise diverse groups with highly heterogeneous histories, cultures, traditions, religions, as well as social and environmental exposures. While the factors captured by these categories contribute to clinical practice and biomedical research, the use of race/ethnicity is widely debated. As a response to this debate, genetic ancestry has been suggested as a complement or alternative to this categorization. However, few studies have examined the effect of genetic ancestry, racial/ethnic identity, and environmental exposures on biological processes. Herein, we examine the contribution of self-identification within ethnicity, genetic ancestry, and environmental exposures on epigenetic modification of DNA methylation, a phenomenon affected by both genetic and environmental factors. We typed over 450,000 variably methylated CpG sites in primary whole blood of 573 individuals of Mexican and Puerto Rican descent who also had high-density genotype data. We found that methylation levels at a large number of CpG sites were significantly associated with ethnicity even when adjusting for genetic ancestry. In addition, we found an enrichment of ethnicity-associated sites amongst loci previously associated with environmental and social exposures. Interestingly, one of the strongest associated sites is driven by the Duffy Null blood type variant, demonstrating a new function of the locus in lymphocytes. Overall, the methylation changes associated with race/ethnicity, driven by both genes and environment, highlight the importance of measuring and accounting for both self-identified race/ethnicity and genetic ancestry in clinical and biomedical studies and the benefits of studying diverse populations. (2) In epigenome-wide association studies (EWAS), different methylation profiles of distinct cell-types may lead to false discoveries. We introduce ReFACTor, a method based on principal component analysis (PCA) for the correction of cell-type heterogeneity in EWAS. ReFACTor does not require knowledge of the cell counts, and it obtains improved estimates of the cell-type composition, resulting in improved power and control for false positives in EWAS.

Project description:(1) In clinical practice and biomedical research populations are often divided categorically into distinct racial and ethnic groups. In reality, these categories comprise diverse groups with highly heterogeneous histories, cultures, traditions, religions, as well as social and environmental exposures. While the factors captured by these categories contribute to clinical practice and biomedical research, the use of race/ethnicity is widely debated. As a response to this debate, genetic ancestry has been suggested as a complement or alternative to this categorization. However, few studies have examined the effect of genetic ancestry, racial/ethnic identity, and environmental exposures on biological processes. Herein, we examine the contribution of self-identification within ethnicity, genetic ancestry, and environmental exposures on epigenetic modification of DNA methylation, a phenomenon affected by both genetic and environmental factors. We typed over 450,000 variably methylated CpG sites in primary whole blood of 573 individuals of Mexican and Puerto Rican descent who also had high-density genotype data. We found that methylation levels at a large number of CpG sites were significantly associated with ethnicity even when adjusting for genetic ancestry. In addition, we found an enrichment of ethnicity-associated sites amongst loci previously associated with environmental and social exposures. Interestingly, one of the strongest associated sites is driven by the Duffy Null blood type variant, demonstrating a new function of the locus in lymphocytes. Overall, the methylation changes associated with race/ethnicity, driven by both genes and environment, highlight the importance of measuring and accounting for both self-identified race/ethnicity and genetic ancestry in clinical and biomedical studies and the benefits of studying diverse populations. (2) In epigenome-wide association studies (EWAS), different methylation profiles of distinct cell-types may lead to false discoveries. We introduce ReFACTor, a method based on principal component analysis (PCA) for the correction of cell-type heterogeneity in EWAS. ReFACTor does not require knowledge of the cell counts, and it obtains improved estimates of the cell-type composition, resulting in improved power and control for false positives in EWAS. Bisulphite converted DNA from 573 samples were hybridised to the Illumina Infinium 450k Human Methylation Beadchip and a complete blood count with automated white blood cell differential was performed by automated flow cytometry for 95 of the samples.

Project description:Background: Mortality from preeclampsia (PE) and PE-associated morbidities are 3-to 5-fold higher in persons of African ancestry than in those of Asian and European ancestries. The placenta is central to the etiology of PE. However, how and to what extent the placenta contributes to worse PE outcomes in persons of African ancestry is yet to be fully elucidated. Objective: We aimed to identify molecular pathways that are unique or enriched in placentas of parturient persons of African ancestry with PE with severe features (sPE) compared to those of Asian and European ancestry with sPE. Study design: Bulk RNA sequencing was performed on 50 placentas from parturient persons with sPE of African (n=9), Asian (n=18) and European (n=23) ancestries and 73 normotensive controls of African (n=9), Asian (n=15) and European (n=49) ancestries. Results: Metabolism, hormone regulation and hypoxia/angiogenesis genes, previously described to be upregulated in PE, including: LEP, PAPPA2, INHA, FSTL3, FLT1, PHYHIP and ENG, were upregulated in sPE across ancestries, with high expression of FSTL3 being additionally associated with intrauterine growth restriction (p<.0001). Notably, LEP, FLT1 and PHYHIP were more highly upregulated in sPE placentas from parturient persons of African versus Asian ancestry. Genes associated with allograft rejection and adaptive immune response were selectively upregulated in placentas from African ancestry parturitions and not in those of Asian and European ancestries. Among the allograft rejection/adaptive immune response genes, IL3RA was of particular interest because the patient with the highest placental IL3RA level, a woman of African ancestry with IL3RA levels 4.5-fold above the average for African ancestry parturitions with sPE, developed postpartum cardiomyopathy, and was the only patient out of 123, that developed this condition. Interestingly, the sPE patients of Asian and European ancestries with the highest IL3RA levels for their ancestries developed unexplained tachycardia peripartum, necessitating echocardiography in the European ancestry patient. The association between elevated placental IL3RA levels and unexplained tachycardia or peripartum cardiomyopathy was found to be significant in the 50 sPE patients (p=.0005). Conclusions: African ancestry parturitions are associated with higher placental upregulation of metabolism (LEP) and hypoxia/angiogenesis (FLT1) genes, and selective upregulation of allograft rejection/adaptive immune response genes, including IL3RA. High placental expression of IL3RA may predict worse maternal cardiovascular outcomes, including peripartum cardiomyopathy. Studies evaluating placental IL3RA levels in peripartum cardiomyopathy cohorts are therefore warranted, as are broader studies evaluating placental factors in maternal cardiovascular outcomes postpartum.

Dataset Information

Accurate ethnicity prediction from placental DNA methylation data

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