Can a 1-week embryo with Mosaicism (MOSAIC), specifically 50% XY and 22 chromosome abnormalities, develop into a normal baby and have a normal pregnancy?

From the Guidelines

It is unlikely that a 1-week embryo with Mosaicism (MOSAIC), specifically 50% XY and 22 chromosome abnormalities, can develop into a normal baby and have a normal pregnancy. Mosaic embryos contain a mixture of chromosomally normal and abnormal cells, with this specific embryo showing 50% of cells missing chromosome 22 in a male embryo. While some mosaic embryos can lead to healthy pregnancies if the normal cells outcompete the abnormal ones during development, the outcome depends on several factors including the specific chromosome affected, the percentage of abnormal cells, and their distribution in the embryo. Chromosome 22 contains important genes, and complete monosomy 22 is typically lethal, as noted in a study by 1. The incidence of mosaic RATs identified at the time of CVS is 0.6%, and only 2.53% of these cases were confirmed through amniocentesis, indicating a low likelihood of a normal pregnancy outcome in cases of mosaicism 1. Follow-up prenatal diagnostic testing, such as chorionic villus sampling (CVS) or amniocentesis, is recommended to clarify the status of the fetus with respect to the mosaicism detected, as suggested by 1 and 1. The only definitive way to know the outcome is to proceed with transfer and appropriate prenatal testing if pregnancy occurs. Consulting with a reproductive endocrinologist and genetic counselor about your specific case is strongly recommended to understand the potential risks and success rates for your situation. Some key points to consider include:

• The percentage of abnormal cells and their distribution in the embryo
• The specific chromosome affected and its importance in fetal development
• The need for follow-up prenatal diagnostic testing to confirm the presence and extent of mosaicism
• The potential risks and success rates associated with mosaic embryo transfer, as discussed in 1, 1, and 1.

From the Research

Mosaicism in Embryos

• Mosaicism in embryos refers to the presence of two or more cell populations with different genotypes within the same embryo 2, 3.
• The clinical effects of chromosomal mosaicism are directly linked to the type of imbalance, timing of the initial event, distribution of abnormal cells, and ratio of normal/abnormal cells 2.

Implications of Mosaicism on Pregnancy

• Mosaic embryos have reproductive potential for implantation and healthy live birth, with some studies showing live birth rates similar to euploid embryos for those with less than 50% aneuploidy 4, 5.
• However, mosaic embryos have lower implantation rates and higher rates of miscarriage compared to euploid embryos 5.
• The outcome of mosaic embryo transfer is influenced by the amount and type of chromosomal mosaicism present, with some cases resulting in healthy babies and others with persistent chromosomal abnormalities 6, 5.

Specific Case of 50% XY and 22 Chromosome Abnormalities

• There is evidence to suggest that mosaic embryos with specific types of chromosomal abnormalities, such as trisomies, may pose a risk of having a child affected with a trisomy syndrome 3.
• However, the transfer of embryos with mosaic monosomies or other mosaic trisomies is not devoid of risk, and patients must be counseled about the potential risks and outcomes 3.
• In the case of a 1-week embryo with 50% XY and 22 chromosome abnormalities, the likelihood of developing into a normal baby and having a normal pregnancy would depend on various factors, including the type and extent of mosaicism, and should be assessed on a case-by-case basis 2, 5.