Abstract
The first 8 weeks of pregnancy is a critical time, with the majority of pregnancy losses occurring during this period. Abnormal chromosome number (aneuploidy) is a common finding in human miscarriage, yet is rarely reported in domestic animals. Equine early pregnancy loss (EPL) has no diagnosis in over 80% of cases. The aim of this study was to characterise aneuploidies associated with equine EPL. Genomic DNA from clinical cases of spontaneous miscarriage (EPLs; 14–65 days of gestation) and healthy control placentae (various gestational ages) were assessed using a high density genotyping array. Aneuploidy was detected in 12/55 EPLs (21.8%), and 0/15 healthy control placentae. Whole genome sequencing (30X) and digital droplet PCR (ddPCR) validated results. The majority of these aneuploidies have never been reported in live born equines, supporting their embryonic/fetal lethality. Aneuploidies were detected in both placental and fetal compartments. Rodents are currently used to study how maternal ageing impacts aneuploidy risk, however the differences in reproductive biology is a limitation of this model. We present the first evidence of aneuploidy in naturally occurring equine EPLs at a similar rate to human miscarriage. We therefore suggest the horse as an alternative to rodent models to study mechanisms resulting in aneuploid pregnancies.
Highlights
Samples, leading to the theory that certain chromosomes do not tolerate aneuploidy and are embryonic/ fetal lethal
In species with reported live born individuals with autosomal aneuploidies, all are trisomies with no reported monosomies in the literature[28]. This indicates that while some trisomies may be tolerated to term, monosomies are always lethal at some stage during pregnancy
New methods are emerging that may replace karyotyping as gold standard, allowing for higher throughput analysis and diagnosis of aneuploidy, even in degraded conceptus tissues
Summary
Samples, leading to the theory that certain chromosomes do not tolerate aneuploidy and are embryonic/ fetal lethal. In species with reported live born individuals with autosomal aneuploidies, all are trisomies with no reported monosomies in the literature[28] This indicates that while some trisomies may be tolerated to term, monosomies are always lethal at some stage during pregnancy. In order to explore whether aneuploidy is a feature of failed pregnancies in domesticated animal species, we utilised methods previously reported[35] to generate a large bank of conceptuses from naturally occurring clinical cases of EPL in mares. We hypothesised that due to the rarity of aneuploidy in foals born at term, the majority of aneuploidy presents as embryonic/fetal lethal It will be detectable in both placental and fetal compartments of EPL conceptuses consistent with possible origins in maternal meiosis. The primary aim of this study was to quantify the frequency and characteristics of aneuploidy associated with EPL in the mare
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