From the Guidelines
Embryo Mosaicism (MOSAICO) with 50% XY and 22 chromosomes indicates a chromosomal mosaicism where 50% of the analyzed cells show a normal XY sex chromosome pattern, but with an abnormal number of chromosomes, specifically 22 instead of the typical 46, suggesting a potential deletion or loss of genetic material. This condition could potentially affect various aspects of health, including sexual development, fertility, or other developmental issues, depending on the specific genes involved in the deletion. The "M:50%" notation specifically indicates the percentage of cells showing the mosaic pattern, which is crucial for understanding the potential impact on the fetus's health and development 1. Given the complexity of interpreting mosaic results, especially from chorionic villus sampling (CVS), follow-up testing with amniocentesis is recommended to confirm the diagnosis and determine the extent of mosaicism in the fetus 1. It's also important to consult with a medical geneticist or genetic counselor to understand the full implications of this finding, as the clinical significance can vary widely depending on the exact genetic regions affected and the proportion of abnormal cells 2. Key considerations include:
- The potential for the mosaicism to affect fetal development and health
- The need for precise diagnosis through additional testing like amniocentesis
- The importance of genetic counseling to understand the implications and potential outcomes
- The possibility that the mosaicism may be confined to the placenta (confined placental mosaicism, CPM) or truly represent fetal mosaicism (TFM), which has different implications for the fetus's health 1.
From the Research
Definition of Embryo Mosaicism
Embryo mosaicism refers to the presence of two or more cell lines with different genetic makeup within an embryo. This can occur due to various factors, including errors during cell division or the presence of abnormal cells in the placenta.
Understanding MOSAICO with 50% XY and 22 chromosomes
MOSAICO with 50% XY and 22 chromosomes indicates that 50% of the cells in the embryo have a normal XY chromosome pattern, while the other 50% have an extra chromosome 22, resulting in a trisomy 22 condition. This type of mosaicism can be detected through prenatal testing, such as chorionic villus sampling (CVS) or amniocentesis.
Implications of Mosaicism
- The presence of mosaicism can increase the risk of fetal abnormalities, such as growth restriction or birth defects 3, 4.
- However, the risk of fetal involvement and the clinical relevance of an identified mosaic condition depend on various factors, including the type of mosaicism, the level of mosaicism, and the chromosomes involved 5, 6.
- In some cases, mosaicism may be confined to the placenta and not affect the fetus, while in other cases, it may be present in both the placenta and the fetus 7, 6.
Factors Associated with Fetal Mosaicism
- Mosaicism on mesenchymal core culture and the type of chromosome abnormality involved are factors associated with fetal mosaicism 5.
- The level of mosaicism, with higher levels increasing the risk of fetal involvement, is also an important factor 3, 4.
- The presence of uniparental disomy (UPD), which can occur in cases of mosaicism, can also affect the risk of fetal abnormalities 4, 6.
Diagnostic Approaches
- Amniocentesis can be used to confirm the diagnosis of mosaicism and determine the level of mosaicism in the fetus 5, 3, 4, 6.
- Chorionic villus sampling (CVS) can also be used to detect mosaicism, but the results may not always reflect the fetal karyotype 5, 7, 6.
- Array comparative genomic hybridization (aCGH) and fluorescence in situ hybridization (FISH) can be used to detect and quantify mosaicism in uncultured amniocytes 3, 4.