Definition: Uniparental disomy (UPD) is a genetic condition in which an individual inherits two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent.
Overview: Uniparental disomy occurs when a person receives both homologous chromosomes or duplicated copies of a single chromosome from one parent, instead of one copy from each parent as in typical inheritance. This phenomenon can affect any chromosome and may involve the entire chromosome or specific regions. UPD can lead to genetic disorders when it results in either the expression of recessive alleles or the disruption of genomic imprinting, a process where gene expression depends on the parent of origin. Some well-documented syndromes associated with UPD include Prader-Willi syndrome and Angelman syndrome, both of which involve chromosome 15 and are influenced by parental imprinting.
Etymology/Origin: The term "uniparental disomy" is derived from Latin and Greek roots: "uni-" meaning "one," "parental" referring to the parent, and "disomy" meaning "two bodies" or "two chromosomes." Thus, uniparental disomy literally means the presence of two chromosomes from a single parent.
Characteristics: UPD arises through various mechanisms, including gamete complementation, trisomic rescue, monosomic rescue, and post-fertilization errors. There are two main types:
- Heterodisomy: Inheritance of two different homologous chromosomes from one parent, typically due to meiosis I nondisjunction.
- Isodisomy: Inheritance of two identical copies of a single chromosome from one parent, usually due to meiosis II nondisjunction or duplication.
UPD can have clinical consequences in three primary ways:
- Imprinting disorders: When imprinted genes are expressed abnormally due to the absence of the complementary parental contribution.
- Recessive disorders: Isodisomy can unmask recessive mutations if the single chromosome inherited twice carries a pathogenic variant.
- Mosaicism or chromosomal instability: UPD may be associated with underlying chromosomal abnormalities, such as mosaic trisomy.
Detection of UPD typically involves molecular genetic testing, such as microsatellite analysis or single nucleotide polymorphism (SNP) arrays, to determine parental origin of chromosomes.
Related Topics:
- Genomic imprinting
- Prader-Willi syndrome
- Angelman syndrome
- Chromosomal nondisjunction
- Trisomic rescue
- Recessive genetic disorders
- SNP array analysis
- Genetic counseling
UPD is an established concept in medical genetics and is documented in genetic databases and peer-reviewed literature.