Uniparental disomy (UPD) as the cause of inconsistencies in parentage tests: report of maternal UPD of chromosome 2 and review of the literature.

Uniparental disomy (UPD) is the abnormal situation in which both members of a chromosome pair exclusively comprise material of one of the parents. The incidence of UPD is estimated in 1:2000 live births. This rare condition is relevant for medical genetics due to imprinting disorders or recessive diseases; however, it may also impact for parentage testing, leading to apparent false parentage. Herein we report the results of a paternity test in which four inconsistencies were observed, all of them mapped on chromosome 2. To investigate the possibility of a complete maternal compound hetero/isodisomy UPD2 as an alternative to false exclusion paternity result, SNP-array and Y-chromosome haplotyping were additionally performed. The results were compatible with the occurrence of a maternal UPD2. Review of the literature shows that UPD2 represents about half of the UPDs detected in parentage tests. The case reported here illustrates that UPD should be considered in cases of parentage testing exhibiting inconsistencies of at least two markers exclusively in a single chromosome.