Isochromosome

Isochromosome is a type of chromosomal abnormality involving the structure of the chromosome in which the arms of the chromosome are mirror images of each other. This occurs due to an abnormal division of the chromatids during cell division, specifically during the process of meiosis or mitosis. Isochromosomes can lead to genetic disorders because they result in the duplication of one part of the chromosome and the deletion of another, leading to an imbalance in genetic material.

Formation

The formation of an isochromosome occurs during cell division when the centromere, the part of the chromosome that typically holds the two chromatids together, divides along the incorrect plane. Instead of the division occurring longitudinally, resulting in two identical chromatids, it occurs transversely. This results in one chromatid having two long arms and the other having two short arms. The chromatid with two long arms or two short arms forms the isochromosome.

Types

Isochromosomes can be of two main types based on the arms that are duplicated:

• i(18q) - An isochromosome of the long arm of chromosome 18, which can lead to certain abnormalities and developmental delays.
• i(Xq) - An isochromosome of the long arm of the X chromosome, which is associated with Turner syndrome in some cases.

Clinical Significance

Isochromosomes can have various clinical implications depending on which chromosome is affected and the nature of the genetic material that is duplicated or deleted. For example, the presence of an isochromosome i(Xq) can lead to Turner syndrome, a condition characterized by short stature and lack of ovarian development in females. Similarly, other isochromosomes can lead to developmental delays, intellectual disabilities, and physical abnormalities.

Diagnosis

The diagnosis of isochromosome abnormalities is typically made through genetic testing methods such as karyotyping, which allows for the visualization of chromosomes under a microscope, or through more advanced techniques like fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH). These methods can identify the specific structural abnormalities of the chromosomes.

Management

Management of conditions resulting from isochromosome abnormalities depends on the specific disorder and the severity of the symptoms. It often involves a multidisciplinary approach, including medical management of physical health issues, educational and developmental support, and sometimes surgical interventions for associated anomalies.

See Also

• Chromosomal abnormality
• Turner syndrome
• Karyotyping
• Cell division