UNIPARENTAL DISOMY (UPD): A CONSEQUENCE OF NON-DISJUNCTION AND THE IMPLICATIONS IN PRENATAL DIAGNOSIS
Velissariou V*
*Corresponding Author: Dr. Voula Velissariou, Cytogenetics Laboratory, Department of Genetics and Molecular Biology, Mitera Hospital, Erythrou Stavrou 7, Maroussi, Athens 11523, Greece; Tel.: +30-210-686-9869; Fax: +30-210-689-9476; E-mail: voulavel@ hol.gr
page: 55

Abstract

Uniparental disomy (UPD) is the inheritance of both homologous chromosomes from only one parent. It is the result of two events, either two meiotic, or one meiotic and one mitotic, or two mitotic. The phenotypic effect of UPD depends on the chromosome, whether it contains imprinted genes or not, and on its parent of origin. Ad­verse phenotypic effects have been documented for chro­mosomes 6, 7, 11, 12, 14, 15, 16 and 20. Phenotypic ef­fects of UPD can also be due to homozygosity of a reces­sive gene. Fertilization of a disomic gamete, which is a product of non-disjunction, by a gamete monosomic for the same chromosome, and subsequent loss of the normally inherited chromosome (trisomy rescue) is the most fre­quently supposed mechanism of formation, and might result in mosaicism in the placenta, or even in certain tissues of the fetus. This low-level mosaicism can remain undetected and renders the delineation of the phenotype more difficult. Another mechanism that may result in UPD is aberrant chromosome segregation in a cell with a Ro­bertsonian translocation involving chromosomes 14 and 15, which are known to contain imprinted genes. There­fore, when placental mosaicism, or a Robertsonian trans­location are diagnosed prenatally, it raises the question whether the risk of UPD should be considered and tested for in the fetus.

Key words: Genomic imprinting; Prenatal diagnosis; Uniparental disomy (UPD); Mosaicism.




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