Tetrasomy

Tetrasomy is a chromosomal abnormality in which a cell possesses four copies of a particular chromosome, instead of the usual two copies found in diploid cells. This represents a type of aneuploidy, specifically a polysomy. It differs from tetraploidy, where the entire genome is quadrupled.

In tetrasomy, the extra two chromosomes are identical, meaning they are sister chromatids that failed to separate during cell division, usually meiosis. This is distinct from situations where there are two separate, non-identical chromosomes alongside the normal pair. Tetrasomy can occur in any of the 23 chromosome pairs in humans.

The presence of four copies of a chromosome leads to an over-expression of genes located on that chromosome, which can disrupt normal development and function. The severity of the effects depends on the specific chromosome involved and the genes it carries. Tetrasomies are often associated with significant health problems, including developmental delays, intellectual disability, and physical abnormalities.

Diagnosis of tetrasomy typically involves karyotyping or other cytogenetic techniques that can visualize and count chromosomes. Prenatal diagnosis is possible through amniocentesis or chorionic villus sampling.

The prognosis for individuals with tetrasomy varies greatly depending on the specific tetrasomy and the severity of the associated symptoms. Treatment focuses on managing the specific health issues that arise and providing supportive care.

Tetrasomies are relatively rare chromosomal abnormalities. Further research is ongoing to better understand the underlying mechanisms and potential therapeutic interventions.