Uniparental disomy (UPD) describes a condition in which both homologs of a chromosome pair are derived from the same parent. UPD can be associated with phenotypic abnormalities if:
- the chromosome or chromosome segment involved carries genes that are imprinted. Genomic imprinting refers to the differential expression of alleles as determined by the parental origin of the allele.
- homozygosity due to uniparental isodisomy results in the expression of an autosomal recessive condition from a single carrier parent.
UPD7mat has been associated with pre- and postnatal growth retardation and Russell-Silver syndrome. We offer UPD testing of chromosome 7 by microsatellite analysis, which compares microsatellite markers from both parents and the child or fetus. In order for UPD to be determined, a significant number of informative microsatellite markers must be present. Although testing is possible if only one parent is available, the chance of obtaining a sufficient number of informative markers is decreased.
Prenatal UPD studies are appropriate following the detection of a mosaic trisomy or a marker chromosome in a prenatal sample. UPD analysis is also considered when a prenatal test is performed to rule out the possibility that the fetus has inherited an unbalanced translocation from a parent carrying a balanced rearrangement and for pregnancies affected with a de novo translocation.
