Maternal heterodisomy/isodisomy and paternal supernumerary ring of chromosome 7 in a child with Silver-Russell syndrome

Silver-Russell syndrome (SRS) is clinically variable although most cases have several common signs. Different chromosomes and chromosomal regions have been associated with SRS. Maternal uniparental disomy (UPD) of chromosome 7 is responsible for 5-10% of cases, probably because of an imbalance between maternal and paternal imprinted genes and more recently maternal duplication or epimutations in the 11p15 imprinted region have been described. To date, only two patients with maternal UPD7 and a mosaic condition for a supernumerary ring 7 marker have been reported, and we here report a further case. Standard QFQ banding of lymphocytes as well as fluorescence in-situ hybridization analyses were performed to identify and characterize the supernumerary marker. UPD testing was performed on both the patient's and parents' DNA using chromosome 7 microsatellite markers. The patient demonstrated a ring in about 4% of the analysed cells. On the basis of cytogenetic and molecular results, break points were tentatively identified as 7p11.2 and 7q21. Maternal hetero-/iso-UPD and a paternal origin for the supernumerary ring were demonstrated. Clinical data comparison between our patient who has a SRS phenotype and cases with hetero-/iso-UPD7 mat and mosaicism for a paternally derived chromosome 7 ring and previously reported ring 7 cases suggest that the SRS phenotype is probably because of the UPD rather than to the partial trisomy.