Background Maternal uniparental disomy (UPD) of chromosome 7 (upd(7)mat)
accounts for approximately 10% of patients with Silver-Russell syndrome (SRS).
For upd(7)mat and trisomy 7, a significant number of mechanisms have been
proposed to explain the postzygotic formation of these chromosomal
compositions, but all have been based on as small number of cases. To obtain
the ratio of isodisomy and heterodisomy in UPDs (hUPD, iUPD) and to determine
the underlying formation mechanisms, we analysed a large cohort of upd(7)mat
patients (n = 73) by SNP array typing. Based on these data, we discuss the
UPDs and their underlying trisomy 7 formation mechanisms. Results A whole
chromosome 7 maternal iUPD was confirmed in 28.8%, a mixture or complete
maternal hUPD in 71.2% of patients. Conclusions We could demonstrate that
nondisjunction mechanism affecting chromosome 7 are similar to that of the
chromosomes more frequently involved in trisomy (and/or UPD), and that
mechanisms other than trisomic rescue have a lower significance than
previously suspected. Furthermore, we suggest SNP array typing for future
parent- and cell-stage-of origin studies in human aneuploidies as they allow
the definite classification of trisomies and UPDs, and provide information on
recombinational events and their suggested association with aneuploidy
formation
