Disomia

Disomia is a genetic condition characterized by the presence of two copies of a chromosome or chromosome segment inherited from the same parent, rather than one copy from each parent as in normal biparental inheritance. The term originates from Greek roots: "di-" meaning two, and "omus" meaning tumor or mass, referring to the duplication of genetic material.

There are two main types of disomia. Uniparental disomy (UPD) occurs when an individual inherits both copies of a chromosome from one parent and none from the other. This can happen through various mechanisms, such as trisomy rescue, monosomy rescue, or gamete complementation during meiosis. Isodisomy refers to identical copies of a chromosome inherited from one parent, typically resulting from duplication of a single parental chromosome. Heterodisomy involves the inheritance of different homologous chromosomes from the same parent, often due to errors in meiosis I.

Disomia can have significant clinical implications, especially if it leads to the expression of recessive genetic disorders or disrupts normal imprinting mechanisms. Imprinting involves parent-specific gene expression, where certain genes are active only when inherited from a specific parent. Abnormal imprinting caused by disomia can result in developmental disorders or syndromes, such as Prader-Willi or Angelman syndromes, depending on the specific chromosome involved.

Diagnosing disomia typically involves genetic testing methods like microsatellite analysis, array comparative genomic hybridization, or SNP arrays, which can detect uniparental inheritance patterns. Understanding disomia is important in genetic counseling and in the study of hereditary diseases, as it contributes to our knowledge of genetic variation, inheritance errors, and their phenotypic consequences.