Isochromosomi

Isochromosomi are structural abnormalities of chromosomes where a chromosome has duplicated its short (p) or long (q) arm, resulting in a chromosome with two identical arms and a missing opposite arm. This means the chromosome is made up of two copies of one arm and lacks the other.

Isochromosomes arise during cell division, specifically during mitosis or meiosis. The exact mechanism is not fully understood but is thought to involve an abnormal centromere division, where the centromere divides horizontally instead of vertically. This leads to one daughter cell receiving both copies of one arm and the other daughter cell receiving both copies of the other arm.

The presence of isochromosomes can lead to genetic imbalances, as the cell will have an abnormal number of genes on the duplicated arm and a deficiency of genes on the missing arm. This can have various consequences depending on which chromosome is affected and the extent of the imbalance. For example, isochromosomes can be found in certain types of cancer and can also be associated with specific genetic syndromes.

Commonly observed isochromosomes include those of the X chromosome, often seen in Turner syndrome variants, and isochromosomes of chromosome 21, which can contribute to Down syndrome. The clinical manifestations associated with an isochromosome depend on the specific chromosome involved and the resulting genetic imbalance. Genetic testing, such as karyotyping or chromosomal microarray, is used to identify isochromosomes.