uniparental disomy
Summary
Uniparental disomy (UPD) occurs when both copies of a chromosome (or chromosome segment) are inherited from the same parent instead of one from each parent. This can lead to genetic disorders through genomic imprinting effects or unmasking of recessive alleles, with classic examples including Prader-Willi and Angelman syndromes.
Detail
Uniparental disomy results from errors in meiosis or early mitotic divisions, leading to inheritance of both homologous chromosomes from a single parent. There are two types: heterodisomy (both different homologs from one parent) and isodisomy (two copies of the same homolog). UPD can cause disease through three mechanisms: (1) genomic imprinting disorders where parent-of-origin gene expression is disrupted (e.g., maternal UPD15 causes Prader-Willi syndrome, paternal UPD15 causes Angelman syndrome), (2) unmasking recessive mutations when isodisomy occurs (creating functional homozygosity), and (3) disruption of X-inactivation patterns. UPD commonly arises from trisomy rescue (loss of extra chromosome in trisomic conceptus) or monosomy rescue (duplication of single chromosome in monosomic conceptus). Chromosomes 7, 11, 14, and 15 are most clinically significant due to imprinted gene clusters. Diagnosis requires molecular techniques like microsatellite analysis or SNP arrays to determine parental origin of chromosomes.
Sources
- Thompson & Thompson's Genetics in Medicine
- Emery's Elements of Medical Genetics
- USMLE First Aid for the USMLE Step 1
- Human Molecular Genetics by Strachan & Read
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