A study in horses – which share many important similarities with humans in their chromosomes and pregnancies – found that 42% of miscarriages and spontaneous abortions in the first two months of pregnancy were due to complications from an extra set of chromosomes, a condition called triploidy.
‘In that embryonic period [up to eight weeks from conception]triploidy was rarely reported in mammals other than females,” says Mandi de Mestre, professor of equine medicine at Cornell University. “The study tells us that this is likely to be the leading cause of pregnancy loss during the first six weeks of pregnancy. after natural fertilization.”
de Mestre is the corresponding author of “Naturally Occurring Horse Model of Miscarriage Reveals Temporal Relationship Between Chromosomal Aberration Type and Point of Lethality,” published in the Proceedings of the National Academy of Sciences.
Human miscarriages occur in 10-20% of pregnancies and are often associated with chromosomal errors, but there have been no suitable animal models that truly duplicate the characteristics of the condition. The new research results will help veterinarians better understand the causes of pregnancy loss in horses and identify horses as an excellent model for studying human miscarriages.
“We were able to study the impact of chromosome errors throughout gestation in horses,” said de Mestre. “We found that triploidy is only associated with losses during early pregnancy.”
In the study, De Mestre’s laboratory at Cornell, and previously at the Royal Veterinary College in London, received 256 fetus and placenta samples from veterinarians who treated horses with failed pregnancies over a 10-year period. Using the samples, the researchers were able to investigate the prevalence of different types of chromosomal copy number errors associated with pregnancy loss. They found that chromosomal errors occurred in 57.9% of pregnancy losses up to day 55 of pregnancy, in 57.2% of losses between days 56 and 110, and in only 1.4% of losses between day 111 and end of pregnancy. Aneuploidy (loss or gain of a single entire chromosome) was mainly associated with miscarriages in the first ten weeks of pregnancy, while deletions or duplications of only part of a chromosome were found in miscarriages after 110 days. These findings turned out to be remarkably similar to those observed in several large studies in women, the article said.
Horses are a good model for studying human pregnancies because they have a similar gestation period (11 months compared to nine months in women) and the embryo develops at a similar rate in the early stages. Furthermore, horse chromosomes have very similar genetic content to human chromosomes, making them particularly relevant for the study of chromosome errors.
The reasons for miscarriage in women in very early pregnancy are difficult to determine because most fetuses are lost at home during this period, leaving scientists without material – and data – to study. The study’s findings provide insight into the frequency of chromosome errors during the equivalent period of the first six weeks of human pregnancy.
Due to the value of horses and the emotional bond their owners have with them, horses receive a high level of care, with pregnancies routinely monitored, which then provides extensive data for research.
Other animal models, such as mice, are not comparable to human pregnancies. Mice have a gestation period of about three weeks and natural pregnancy losses in mice are low.
In the field of equine health, the study provides new details on common chromosomal abnormalities that are likely to change the clinical management of pregnancies. For example, if a doctor determines that a horse has a major chromosomal error, he may no longer choose to prolong the pregnancy by administering hormones, which is common in pregnant mares. The study will also direct researchers to develop new diagnostic tests for chromosome abnormalities in equine fetuses and investigate molecular mechanisms that lead to these abnormalities.
“This research has provided a foundation for understanding the genetic causes of pregnancy loss in horses, often referred to as pregnancy loss of unknown cause,” said Shebl Salem, a postdoctoral researcher in de Mestre’s Equine Pregnancy Lab and co-first author of the book. study.
Other co-first authors include Jessica Lawson of the Royal Veterinary College in London, United Kingdom; and Donald Miller, de Mestre laboratory manager.
The research was funded in part by the Horserace Betting Levy Board and Thoroughbred Breeders Association.
