Our straightforward algorithms for characterization of the origin of an sSMC has the advantages that it can be performed without the use of sophisticated or highly specialized equipment, except for one- or two-color-FISH and that it provides the chromosomal origin of a sSMC. Moreover, if molecular genetic approaches such as micro satellite analysis are available, a possible disease-causing UPD can be excluded. However, only subcenM-FISH [15] or array-CGH (comparative genomic hybridization) [22] can exclude or detect a small partial tri- or polysomy of the centromere-near region of the sSMC. In most cases, after exclusion of an UPD of an sSMC’s sister chromosome, such an imbalance determines the clinical effect of the marker chromosome [16]. When possibilities for determination of the euchromatic contents of an sSMC are not available, all reported sSMC cases (sorted by chromosomal origin) can be found on the sSMC homepage [9]. The authors welcome the opportunity to characterize sSMC cases by subcenM-FISH or other approaches.