From the Guidelines
Mosaic trisomy is a genetic condition where a mixture of normal and abnormal cells with an extra chromosome is present, resulting in a variable severity of symptoms depending on the affected chromosome and proportion of abnormal cells. This condition is less severe than full trisomy, where all cells have the extra chromosome, as noted in the context of noninvasive prenatal screening results 1. Key points about mosaic trisomy include:
- It's less severe than full trisomy, where all cells have the extra chromosome.
- Symptoms and severity vary widely depending on which chromosome is affected and the proportion of cells with the extra copy.
- Common examples include mosaic Down syndrome (trisomy 21) and mosaic Turner syndrome (monosomy X with some normal cells).
- Diagnosis typically involves genetic testing, such as karyotyping or chromosomal microarray analysis, as recommended for follow-up prenatal diagnostic testing after positive noninvasive prenatal screening results 1.
- Treatment is supportive and depends on the specific symptoms present, with a focus on medical management, developmental therapies, and regular monitoring.
- Prognosis is generally better than in full trisomy cases, but varies significantly between individuals, highlighting the importance of genetic counseling and managing potential health issues associated with the condition 1. Understanding mosaic trisomy is crucial for genetic counseling and managing potential health issues associated with the condition, as the mosaic nature of the condition explains why symptoms can be milder or more variable compared to full trisomy cases.
From the Research
Definition of Mosaic Trisomy
Mosaic trisomy is a genetic condition where a mixture of normal and abnormal cells with an extra chromosome is present [(2,3,4,5,6)]. This condition occurs when there are two different cell lines in the same individual, one with a normal number of chromosomes and the other with an extra chromosome.
Characteristics of Mosaic Trisomy
The characteristics of mosaic trisomy vary greatly depending on the specific chromosome involved and the percentage of abnormal cells [(2,3,4,5,6)]. Some common features of mosaic trisomy include:
- Dysmorphic features, such as short stature, cubitus valgus, and congenital heart defects [(2,3,4,6)]
- Developmental delays and intellectual disability [(2,3,4,5)]
- Variable intellectual capabilities, ranging from profound mental retardation to above average intelligence 2
- Increased risk of congenital anomalies, such as microcephaly, delayed bone age, and brachydactyly [(2,4,5)]
Types of Mosaic Trisomy
There are several types of mosaic trisomy, including:
- Mosaic trisomy 18, which is characterized by a variable phenotype, ranging from normal intelligence and no significant dysmorphic features to severe developmental delays and congenital anomalies 2
- Mosaic trisomy 22, which is associated with developmental delays, intellectual disability, and dysmorphic features 3
- Mosaic trisomy 5, which is a rare condition that can result in multiple congenital anomalies and uniparental disomy 5 4
- Trisomy 9 mosaic syndrome, which is characterized by multiorgan system involvement, including craniofacial dysmorphisms, cardiac, genitourinary, skeletal, and central nervous system abnormalities 5
- Mosaic trisomy 13, which is associated with a variable phenotype, ranging from a less severe phenotype with longer survival to a more severe phenotype with early death 6
Diagnosis and Management
Diagnosis of mosaic trisomy is typically made through chromosomal analysis, such as karyotyping or microarray analysis [(2,3,4,5,6)]. Management of mosaic trisomy depends on the specific characteristics of the individual and may include genetic counseling, medical management of congenital anomalies, and developmental therapy [(2,3,4,5,6)].