Uniparental disomy

Uniparental Disomy

Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent. This genetic anomaly can lead to various health issues depending on the specific chromosomes involved and whether the disomy is isodisomy or heterodisomy.

Types of Uniparental Disomy

Uniparental disomy can be classified into two main types:

Isodisomy

Isodisomy occurs when an individual inherits two identical copies of a chromosome from one parent. This can result from a duplication of a single chromosome from one parent. Isodisomy can lead to the expression of recessive genetic disorders if the duplicated chromosome carries a recessive allele.

Heterodisomy

Heterodisomy occurs when an individual inherits two different homologous chromosomes from one parent. This usually results from a nondisjunction event during meiosis I. Heterodisomy can lead to imprinting disorders if the chromosomes involved are subject to genomic imprinting.

Causes of Uniparental Disomy

Uniparental disomy can arise from several mechanisms, including:

• Trisomy Rescue: This is the most common mechanism, where a trisomic zygote loses one chromosome to restore a normal diploid number, potentially resulting in UPD if the remaining chromosomes are from the same parent.
• Monosomy Rescue: A monosomic zygote duplicates its single chromosome to restore diploidy, leading to isodisomy.
• Gamete Complementation: This occurs when a gamete with no copies of a chromosome is fertilized by a gamete with two copies.

Clinical Implications

The clinical consequences of UPD depend on the specific chromosomes involved and whether the genes on those chromosomes are subject to genomic imprinting. Some known conditions associated with UPD include:

• Prader-Willi Syndrome: Often caused by maternal uniparental disomy of chromosome 15.
• Angelman Syndrome: Can result from paternal uniparental disomy of chromosome 15.
• Beckwith-Wiedemann Syndrome: Associated with paternal uniparental disomy of chromosome 11.

Diagnosis

Diagnosis of UPD typically involves genetic testing, such as:

• Karyotyping: To identify chromosomal abnormalities.
• Molecular Genetic Testing: Techniques like SNP arrays or microsatellite analysis can detect UPD by identifying regions of homozygosity or lack of heterozygosity.

Related Pages

• Genomic imprinting
• Chromosomal abnormalities
• Genetic disorders

• Animation of uniparental isodisomy
  Animation of uniparental isodisomy