What is the likelihood of a normal baby developing from a 1-week embryo with Mosaicism (MOSAIC), specifically XY -22 (with 50% mosaicism), prior to embryo transfer?

From the Guidelines

There is a low likelihood that a 1-week embryo with Mosaicism (MOSAIC), specifically XY -22 (with 50% mosaicism), will develop into a normal baby after transfer, due to the high risk of miscarriage, birth defects, or developmental issues associated with monosomy 22. The presence of mosaicism, where 50% of the cells show a loss of chromosome 22, indicates a mixture of normal and abnormal cells, which can lead to various complications during pregnancy and fetal development 1. The specific chromosome affected, in this case, chromosome 22, and the percentage of abnormal cells, play a significant role in determining the developmental potential of the embryo. Some key points to consider include:

• Monosomy 22 is typically considered a severe abnormality, and the mosaic nature of the embryo means that some cells are normal, while others are not 1.
• The embryo's ability to self-correct or segregate abnormal cells to the placenta can influence the outcome, but this is unpredictable and cannot be relied upon 1.
• Comprehensive genetic counseling is essential to understand the risks associated with transferring a mosaic embryo, including potential developmental issues, miscarriage, or birth defects 1.
• Close monitoring throughout pregnancy would be crucial if implantation occurs, to detect any potential complications early on. Given the limited evidence and undetermined clinical utility of noninvasive prenatal screening (NIPS) for rare disorders like monosomy 22, consultation with a genetics healthcare professional is prudent before proceeding with transfer 1.

From the Research

Mosaicism and Embryo Development

The likelihood of a normal baby developing from a 1-week embryo with Mosaicism (MOSAIC), specifically XY -22 (with 50% mosaicism), prior to embryo transfer is influenced by several factors, including the type of chromosomal imbalance, the timing of the initial event leading to mosaicism, and the distribution of abnormal cells throughout the body 2.

Factors Affecting Mosaicism

• The type of chromosomal imbalance (size, gene content, and copy number) affects the clinical outcome of mosaicism 2
• The timing of the initial event leading to mosaicism during embryogenesis/fetal development influences the distribution of abnormal cells in the body 2
• The ratio of normal/abnormal cells within each tissue also plays a crucial role in determining the clinical outcome of mosaicism 2
• Assay noise and culture artifacts can impact the significance and management of mosaic cases 2

Detection of Mosaicism

• Non-invasive prenatal testing (NIPT) can detect fetoplacental chromosomal mosaicism, but has a low detection rate, especially for low-level mosaicism 3, 4
• Chorionic villus sampling (CVS) and amniocentesis can also detect mosaicism, but may not always reflect the true fetal karyotype 5, 6
• The detection of mosaicism can be influenced by the level of mosaicism, with high-level mosaicism more likely to be detected by NIPT 4

Clinical Outcome of Mosaicism

• The clinical outcome of mosaicism can vary widely, ranging from normal development to adverse pregnancy outcomes, such as intrauterine growth restriction (IUGR) and congenital anomalies 5, 6
• The presence of mosaicism can also increase the risk of uniparental disomy (UPD), which can have significant clinical implications 6
• In some cases, low-level mosaicism may be associated with a favorable fetal outcome, despite the presence of adverse pregnancy outcomes, such as IUGR 6