Maternal uniparental disomy (UPD) for chromosome 2 discovered by exclusion of paternity.

Serological and molecular (DNA-STR) analysis of a paternity case demonstrated exclusion of paternity of the presumptive father in two markers (ACP and Apo B, both localized on chromosome 2, region 2p25.2 and 2p23/24, respectively) in a phenotypically normal girl with a normal karyotype 46,XX (by GT-banding). The index of paternity calculated for other serological (seven erythrocyte antigens, six serum protein systems, and seven isozymes, as well as the A- and B-HLA loci) and nine DNA markers, excluding ACP and Apo B, gives a very high (virtually certain) degree of paternity for the presumptive father. Maternal uniparental disomy (UPD) for chromosome 2 was suspected. Evaluation of polymorphic DNA markers (STRs) spanning chromosome 2 of the child, mother, and presumptive father demonstrated that the girl had inherited two maternal chromosome 2 homologues, whereas alleles for markers from other chromosomes were inherited from the father in a Mendelian fashion. The girl was homoallelic for informative markers mapping to the chromosomal regions 2p23-25, but she was heteroallelic for informative markers on the long arm of chromosome 2, establishing that the maternal UPD with partial isodisomy of the short arm was caused by a meiosis I nondisjunction event with genetic recombination (chiasmata in this region 2p23-25) during oogenesis.